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12 changes: 9 additions & 3 deletions Makefile
Original file line number Diff line number Diff line change
@@ -1,7 +1,13 @@
all: kilo
CC = gcc -g -Wall -W -ansi -pedantic -std=c99 -pthread -o
C+ = g++ -g -Wall -pthread -std=c++11 -o

all: kilo server

kilo: kilo.c
$(CC) -o kilo kilo.c -Wall -W -pedantic -std=c99
$(CC) kilo kilo.c

server: server.cpp
$(C+) server server.cpp

clean:
rm kilo
rm -f kilo server transfer
5 changes: 4 additions & 1 deletion README.md
Original file line number Diff line number Diff line change
Expand Up @@ -6,8 +6,11 @@ Kilo is a small text editor in less than 1K lines of code (counted with cloc).
A screencast is available here: https://asciinema.org/a/90r2i9bq8po03nazhqtsifksb

Usage: kilo `<filename>`
New Usage: kilo <host> <port>

Keys:
'get' to copy file from server
Comment on lines 8 to +11

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⚠️ Potential issue | 🟡 Minor

Documentation is inconsistent with the new implementation.

The old usage kilo <filename> on line 8 no longer works since main() in kilo.c now requires exactly 2 arguments (host and port). Additionally, the 'get' command must be typed in stdin before the editor UI starts, which isn't clear from this documentation.

Consider updating to clarify the workflow:

  1. Run kilo <host> <port> to connect to the server
  2. Type get (then press Enter) to download a file
  3. Press Ctrl+D (EOF) to exit the stdin loop and launch the editor
🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed.

In `@README.md` around lines 8 - 11, The README still shows the old usage `kilo
<filename>` but main() in kilo.c now requires two args (host and port), so
update the Usage section to `kilo <host> <port>` and add a short workflow
explaining that after connecting you must type the `get` command (then Enter)
into stdin to request a file, and then press Ctrl+D (EOF) to exit the stdin loop
and launch the editor UI; mention main() and the `get` stdin requirement so
readers know the sequence.


Editor Keys:

CTRL-S: Save
CTRL-Q: Quit
Expand Down
10 changes: 0 additions & 10 deletions TODO

This file was deleted.

91 changes: 85 additions & 6 deletions kilo.c
Original file line number Diff line number Diff line change
Expand Up @@ -53,6 +53,7 @@
#include <stdarg.h>
#include <fcntl.h>
#include <signal.h>
#include <netdb.h>

/* Syntax highlight types */
#define HL_NORMAL 0
Expand Down Expand Up @@ -109,6 +110,8 @@ struct editorConfig {
struct editorSyntax *syntax; /* Current syntax highlight, or NULL. */
};

//Note: we may want to add a few fields to the erow and editorConfig structs

static struct editorConfig E;

enum KEY_ACTION{
Expand Down Expand Up @@ -198,6 +201,7 @@ struct editorSyntax HLDB[] = {
#define HLDB_ENTRIES (sizeof(HLDB)/sizeof(HLDB[0]))

/* ======================= Low level terminal handling ====================== */
//Note: probably don't need to edit these

static struct termios orig_termios; /* In order to restore at exit.*/

Expand All @@ -214,7 +218,7 @@ void editorAtExit(void) {
disableRawMode(STDIN_FILENO);
}

/* Raw mode: 1960 magic shit. */
/* Raw mode: 1960 magic*/
int enableRawMode(int fd) {
struct termios raw;

Expand Down Expand Up @@ -362,6 +366,7 @@ int getWindowSize(int ifd, int ofd, int *rows, int *cols) {
}

/* ====================== Syntax highlight color scheme ==================== */
//Note: probably don't need to edit these

int is_separator(int c) {
return c == '\0' || isspace(c) || strchr(",.()+-/*=~%[];",c) != NULL;
Expand Down Expand Up @@ -551,6 +556,10 @@ void editorSelectSyntaxHighlight(char *filename) {
}

/* ======================= Editor rows implementation ======================= */
//Note: probably want to edit these. perhaps at the end of an update function, we call another
// function to send an update message to the server.
//Note: we can copy the logic from these functions to allow for editing after receuving an
// update message from the server.

/* Update the rendered version and the syntax highlight of a row. */
void editorUpdateRow(erow *row) {
Expand Down Expand Up @@ -616,7 +625,7 @@ void editorFreeRow(erow *row) {
free(row->hl);
}

/* Remove the row at the specified position, shifting the remainign on the
/* Remove the row at the specified position, shifting the remaining on the
* top. */
void editorDelRow(int at) {
erow *row;
Expand Down Expand Up @@ -852,6 +861,7 @@ int editorSave(void) {
}

/* ============================= Terminal update ============================ */
//Note: probably don't need to edit these

/* We define a very simple "append buffer" structure, that is an heap
* allocated string where we can append to. This is useful in order to
Expand Down Expand Up @@ -1008,6 +1018,7 @@ void editorSetStatusMessage(const char *fmt, ...) {
}

/* =============================== Find mode ================================ */
//Note: probably don't need to edit these

#define KILO_QUERY_LEN 256

Expand Down Expand Up @@ -1107,6 +1118,7 @@ void editorFind(int fd) {
}

/* ========================= Editor events handling ======================== */
//Note: we probably don't need to edit these

/* Handle cursor position change because arrow keys were pressed. */
void editorMoveCursor(int key) {
Expand Down Expand Up @@ -1288,14 +1300,81 @@ void initEditor(void) {
signal(SIGWINCH, handleSigWinCh);
}

/* ========================= Communication with Server ======================== */

void receiveFile(int fd){
ssize_t n;
FILE *file = fopen("transfer", "w");
char buffer[1024];

n = read(fd, buffer, 1024);
buffer[n] = '\0';
Comment on lines +1310 to +1311

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🔴 receiveFile: out-of-bounds write when read() returns -1

At kilo.c:1310-1311, if read(fd, buffer, 1024) returns -1 (error), then n is -1 and buffer[n] writes to buffer[-1], which is an out-of-bounds memory write. The return value of read() must be checked before using it as an index.

Suggested change
n = read(fd, buffer, 1024);
buffer[n] = '\0';
n = read(fd, buffer, 1023);
if (n <= 0) return;
buffer[n] = '\0';
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while (1){
if ((n = read(fd, buffer, 1024)) > 0){
// printf("Line: %s\n", buffer);
buffer[n] = '\0';
if (!strcmp(buffer, "End Transfer")){
// printf("Closing\n");
fclose(file);
return;
}
fprintf(file, "%s\n", buffer);
send(fd, "ACK", 1024, 0); //why are we sending this?

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🔴 send() reads 1024 bytes from a 4-byte "ACK" string literal, causing buffer over-read

send(fd, "ACK", 1024, 0) transmits 1024 bytes from a 4-byte string literal, reading ~1020 bytes of unrelated memory and sending it over the network.

Suggested change
send(fd, "ACK", 1024, 0); //why are we sending this?
send(fd, "ACK", strlen("ACK"), 0);
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}
}
Comment on lines +1313 to +1325

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🚩 TCP stream semantics not handled — no message framing

The entire client-server protocol assumes that each send() corresponds to exactly one read() on the other side, with matching boundaries. TCP is a byte stream, not a message-oriented protocol — a single read() may return partial data from one send or combined data from multiple sends. Without proper message framing (e.g., length-prefixed messages or delimiters), the protocol is fundamentally unreliable. For example, the "End Transfer" sentinel at the client side (kilo.c:1317) could arrive split across two reads, or merged with the previous line's data.

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//editorOpen("test");
}
Comment on lines +1305 to +1327

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⚠️ Potential issue | 🔴 Critical

Critical: Buffer overread and missing error handling in receiveFile().

Several issues need to be addressed:

  1. Buffer overread (Line 1323): send(fd, "ACK", 1024, 0) attempts to send 1024 bytes, but "ACK" is only a 4-byte string literal (including null terminator). This reads uninitialized/invalid memory beyond the string.

  2. No error handling for fopen() (Line 1307): If the file cannot be created, file will be NULL and subsequent fprintf/fclose calls will crash.

  3. Potential buffer underflow (Lines 1311, 1316): If read() returns -1 on error, buffer[n] = '\0' becomes buffer[-1] = '\0', which is undefined behavior.

  4. First read result unused (Line 1310-1311): The "Start Transfer" marker is read but never validated.

🐛 Proposed fix
 void receiveFile(int fd){
 	ssize_t n;
 	FILE *file = fopen("transfer", "w");
+	if (!file) {
+		perror("Failed to open transfer file");
+		return;
+	}
 	char buffer[1024];
 
 	n = read(fd, buffer, 1024);
-	buffer[n] = '\0';
+	if (n <= 0) {
+		fclose(file);
+		return;
+	}
+	buffer[n] = '\0';
+	// Optionally validate: strcmp(buffer, "Start Transfer") == 0
 
 	while (1){
 		if ((n = read(fd, buffer, 1024)) > 0){
 			// printf("Line: %s\n", buffer);
 			buffer[n] = '\0';
 			if (!strcmp(buffer, "End Transfer")){
 				// printf("Closing\n");
 				fclose(file);
 				return;
 			}
 			fprintf(file, "%s\n", buffer);
-			send(fd, "ACK", 1024, 0); //why are we sending this?
+			send(fd, "ACK", 3, 0);
 		}
 	}
 	//editorOpen("test");
 }
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
void receiveFile(int fd){
ssize_t n;
FILE *file = fopen("transfer", "w");
char buffer[1024];
n = read(fd, buffer, 1024);
buffer[n] = '\0';
while (1){
if ((n = read(fd, buffer, 1024)) > 0){
// printf("Line: %s\n", buffer);
buffer[n] = '\0';
if (!strcmp(buffer, "End Transfer")){
// printf("Closing\n");
fclose(file);
return;
}
fprintf(file, "%s\n", buffer);
send(fd, "ACK", 1024, 0); //why are we sending this?
}
}
//editorOpen("test");
}
void receiveFile(int fd){
ssize_t n;
FILE *file = fopen("transfer", "w");
if (!file) {
perror("Failed to open transfer file");
return;
}
char buffer[1024];
n = read(fd, buffer, 1024);
if (n <= 0) {
fclose(file);
return;
}
buffer[n] = '\0';
// Optionally validate: strcmp(buffer, "Start Transfer") == 0
while (1){
if ((n = read(fd, buffer, 1024)) > 0){
// printf("Line: %s\n", buffer);
buffer[n] = '\0';
if (!strcmp(buffer, "End Transfer")){
// printf("Closing\n");
fclose(file);
return;
}
fprintf(file, "%s\n", buffer);
send(fd, "ACK", 3, 0);
}
}
//editorOpen("test");
}
🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed.

In `@kilo.c` around lines 1305 - 1327, In receiveFile(), fix unsafe reads and
missing checks: verify fopen("transfer", "w") succeeded and handle/return on
NULL before using file; check each read() return (n) for <=0 and handle
errors/EOF (do not write buffer[n] when n<=0); validate the initial read result
and confirm it contains the expected "Start Transfer" marker before proceeding;
replace send(fd, "ACK", 1024, 0) with sending the actual ACK length (e.g., use
strlen or sizeof on the ACK literal) and check its return for errors; ensure
fclose(file) only called if file was successfully opened.


/* ============================= Main Program ================================== */

//main program of text-editor client
int main(int argc, char **argv) {
if (argc != 2) {
fprintf(stderr,"Usage: kilo <filename>\n");
//check command-line args
if (argc != 3) {
fprintf(stderr,"Usage: kilo <host> <port>\n");
exit(1);
}

initEditor();
editorSelectSyntaxHighlight(argv[1]);
//setup
struct addrinfo hints, *res, *traverser;
memset(&hints, 0, sizeof(struct addrinfo));
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
int r = getaddrinfo(argv[1], argv[2], &hints, &res);
if (r != 0){
fprintf(stderr,"Error: Can't find server.\n");
return 1;
}

// Try addresses until one is successful
int serverFd;
for (traverser = res; traverser; traverser = traverser->ai_next){
if ((serverFd = socket(traverser->ai_family, traverser->ai_socktype, traverser->ai_protocol)) != -1){
if ((connect(serverFd, traverser->ai_addr, traverser->ai_addrlen)) == 0){
break;
}
}
}
printf("Connected\n");
Comment on lines +1358 to +1359

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🔴 No check for connection failure after address traversal loop

At kilo.c:1352-1358, if none of the addresses from getaddrinfo result in a successful connection, the loop ends with traverser == NULL but the code proceeds to print "Connected" and use serverFd (which may hold a failed socket or be from a socket() call that succeeded but connect() failed). There is no check for traverser == NULL to detect that all connection attempts failed.

Suggested change
}
printf("Connected\n");
}
if (!traverser) {
fprintf(stderr, "Error: Could not connect to server.\n");
freeaddrinfo(res);
return 1;
}
freeaddrinfo(res);
printf("Connected\n");
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Comment on lines +1351 to +1359

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⚠️ Potential issue | 🟠 Major

Missing connection failure check and resource cleanup.

  1. No success check: After the loop, traverser could be NULL if all addresses failed, but the code prints "Connected" and continues anyway.

  2. Socket leak: On connect() failure, the socket serverFd isn't closed before trying the next address.

  3. Memory leak: freeaddrinfo(res) is never called to free the address list.

🔧 Proposed fix
 	// Try addresses until one is successful
 	int serverFd;
 	for (traverser = res; traverser; traverser = traverser->ai_next){
 		if ((serverFd = socket(traverser->ai_family, traverser->ai_socktype, traverser->ai_protocol)) != -1){
 			if ((connect(serverFd, traverser->ai_addr, traverser->ai_addrlen)) == 0){
 				break;
 			}
+			close(serverFd);
 		}
 	}
+	freeaddrinfo(res);
+	if (!traverser) {
+		fprintf(stderr, "Error: Could not connect to server.\n");
+		return 1;
+	}
 	printf("Connected\n");
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
int serverFd;
for (traverser = res; traverser; traverser = traverser->ai_next){
if ((serverFd = socket(traverser->ai_family, traverser->ai_socktype, traverser->ai_protocol)) != -1){
if ((connect(serverFd, traverser->ai_addr, traverser->ai_addrlen)) == 0){
break;
}
}
}
printf("Connected\n");
int serverFd;
for (traverser = res; traverser; traverser = traverser->ai_next){
if ((serverFd = socket(traverser->ai_family, traverser->ai_socktype, traverser->ai_protocol)) != -1){
if ((connect(serverFd, traverser->ai_addr, traverser->ai_addrlen)) == 0){
break;
}
close(serverFd);
}
}
freeaddrinfo(res);
if (!traverser) {
fprintf(stderr, "Error: Could not connect to server.\n");
return 1;
}
printf("Connected\n");
🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed.

In `@kilo.c` around lines 1351 - 1359, The loop that creates sockets and calls
connect (using serverFd and traverser from res) lacks failure handling and
cleanup: ensure that when connect() fails you close(serverFd) before trying the
next traverser, and after the loop check whether traverser is non-NULL
(connection succeeded) before printing "Connected" or proceeding; if traverser
is NULL return/handle the connection error and do not use serverFd. Finally
always call freeaddrinfo(res) after the connection attempt (whether it succeeded
or failed) to free the address list.


char buffer[1024];
while (fgets(buffer, 1024, stdin)){
buffer[strcspn(buffer, "\r\n")] = 0;
if (!strcmp(buffer, "get")){
printf("sending get\n");
send(serverFd, "get", 1024, 0);

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🔴 send() reads 1024 bytes from a 4-byte string literal, causing buffer over-read

send(serverFd, "get", 1024, 0) at kilo.c:1366 tells send() to transmit 1024 bytes starting from the address of the string literal "get", which is only 4 bytes (including the null terminator). This reads ~1020 bytes past the string literal, leaking arbitrary program memory to the network peer (similar to the Heartbleed vulnerability). The same class of bug exists at kilo.c:1323 with "ACK".

Suggested change
send(serverFd, "get", 1024, 0);
send(serverFd, "get", strlen("get"), 0);
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⚠️ Potential issue | 🔴 Critical

Buffer overread when sending "get" command.

Same issue as in receiveFile(): send(serverFd, "get", 1024, 0) sends 1024 bytes but the string literal "get" is only 4 bytes (including null terminator). This reads uninitialized memory.

🐛 Proposed fix
-			send(serverFd, "get", 1024, 0);
+			send(serverFd, "get", 3, 0);
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
send(serverFd, "get", 1024, 0);
send(serverFd, "get", 3, 0);
🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed.

In `@kilo.c` at line 1366, The send call is writing 1024 bytes from the string
literal "get", causing a buffer overread; replace send(serverFd, "get", 1024, 0)
with a length-limited call that sends only the actual bytes (e.g.,
send(serverFd, "get", sizeof("get") or strlen("get"), 0)) so it doesn't read
past the string literal—update the call site that currently uses send(serverFd,
"get", 1024, 0) (same pattern as the one fixed in receiveFile()) to use the
correct length.

receiveFile(serverFd);
}
// printf("%s\n", buffer);
}

close(serverFd);
// exit(0);

//start editor
initEditor();
editorSelectSyntaxHighlight("transfer");
editorOpen(argv[1]);

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🔴 editorOpen(argv[1]) opens hostname as file instead of the received "transfer" file

At kilo.c:1378, editorOpen(argv[1]) opens argv[1] (the server hostname) as a file. The file was received from the server into "transfer" (kilo.c:1307), and syntax highlighting is correctly set up for "transfer" (kilo.c:1377), but editorOpen opens the wrong file. This should be editorOpen("transfer").

Suggested change
editorOpen(argv[1]);
editorOpen("transfer");
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Comment on lines +1376 to 1378

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⚠️ Potential issue | 🔴 Critical

Critical: Editor opens wrong file after transfer.

Line 1378 calls editorOpen(argv[1]) which attempts to open the host argument (e.g., "localhost") as a file, not the transferred "transfer" file. This will fail to find the file or open an unrelated file.

🐛 Proposed fix
     //start editor
 	initEditor();
     editorSelectSyntaxHighlight("transfer");
-    editorOpen(argv[1]);
+    editorOpen("transfer");
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
initEditor();
editorSelectSyntaxHighlight("transfer");
editorOpen(argv[1]);
initEditor();
editorSelectSyntaxHighlight("transfer");
editorOpen("transfer");
🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed.

In `@kilo.c` around lines 1376 - 1378, The editor is opening the host argument
because editorOpen(argv[1]) uses the host string; update the call in the init
sequence (initEditor, editorSelectSyntaxHighlight) to open the transferred file
instead of argv[1] — e.g., replace editorOpen(argv[1]) with
editorOpen("transfer") or pass the actual transfer filename variable if one
exists so editorOpen opens the received "transfer" file rather than the host
argument.

enableRawMode(STDIN_FILENO);
editorSetStatusMessage(
Comment on lines +1375 to 1380

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🚩 Editor code is unreachable after stdin EOF-based command loop

In kilo.c:1362-1384, the main function first enters a while (fgets(buffer, 1024, stdin)) loop to read commands. This loop only terminates when fgets returns NULL (stdin reaches EOF or error). After the loop, the code attempts to start the interactive editor at line 1376-1384, which reads keypresses from STDIN_FILENO. Since stdin is already at EOF, editorReadKey at kilo.c:260 will get read() returning 0 indefinitely (or -1), making the editor completely non-functional. The entire editor section after close(serverFd) is effectively dead code in this flow. The architecture needs rethinking — perhaps the command loop and editor should use separate input mechanisms, or the editor should be started before the fgets loop.

(Refers to lines 1375-1385)

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Expand Down
143 changes: 143 additions & 0 deletions server.cpp
Original file line number Diff line number Diff line change
@@ -0,0 +1,143 @@
// C Headers
#include <arpa/inet.h>
#include <errno.h>
#include <netdb.h>
#include <netinet/in.h>
#include <pthread.h>
#include <signal.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <unistd.h>
// C++ Headers
#include <fstream>
#include <iostream>
#include <sstream>
#include <map>
#include <string>
#include <vector>
using namespace std;

//readFile - reads lines in file into the data structure lines
vector<string> readFile(){
string line;
vector<string> lines;
ifstream file("test");
while (getline(file, line)){
lines.push_back(line);
}
return lines;
}
Comment on lines +23 to +31

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⚠️ Potential issue | 🟡 Minor

File stream not checked for open failure.

readFile() doesn't check if opening the file "test" succeeded. If the file doesn't exist, the function returns an empty vector silently, and the client receives only the transfer markers with no content.

💡 Suggested improvement
 vector<string> readFile(){
 	string line;
 	vector<string> lines;
 	ifstream file("test");
+	if (!file.is_open()) {
+		cerr << "Error: Could not open file 'test'" << endl;
+		return lines;
+	}
 	while (getline(file, line)){
 		lines.push_back(line);
 	}
 	return lines;
 }
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
vector<string> readFile(){
string line;
vector<string> lines;
ifstream file("test");
while (getline(file, line)){
lines.push_back(line);
}
return lines;
}
vector<string> readFile(){
string line;
vector<string> lines;
ifstream file("test");
if (!file.is_open()) {
cerr << "Error: Could not open file 'test'" << endl;
return lines;
}
while (getline(file, line)){
lines.push_back(line);
}
return lines;
}
🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed.

In `@server.cpp` around lines 23 - 31, readFile currently opens ifstream
file("test") and proceeds without verifying the stream; add an explicit check on
file.is_open() (or file.good()) after constructing ifstream in readFile and
handle failures by returning an error or logging and propagating (e.g., throw
runtime_error or return an optional/error code) so the caller can detect the
open failure instead of silently returning an empty vector; update the behavior
around readFile() usage to handle the new error path accordingly.


//sendFile - send file line-by-line to a client at fd
void sendFile(int fd, vector<string> lines){
vector<string>::iterator i;

send(fd, (void*)"Start Transfer", 1024, 0);

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🔴 send() reads 1024 bytes from 15-byte and 13-byte string literals in sendFile

send(fd, (void*)"Start Transfer", 1024, 0) at server.cpp:37 transmits 1024 bytes from a 15-byte string literal, reading ~1009 bytes of unrelated memory. Same issue at server.cpp:55 with "End Transfer" (13 bytes). Both leak memory contents to the client.

Suggested change
send(fd, (void*)"Start Transfer", 1024, 0);
send(fd, (void*)"Start Transfer", strlen("Start Transfer"), 0);
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/* for (i = lines.begin(); i != lines.end(); i++){
char buffer[1024];
string msg = *i;
// cout << "Line: " << msg << endl;
send(fd, msg.c_str(), msg.length(), 0);
read(fd, buffer, 1024);
} */

//this is the same as the loop that is commented out
for(string msg : lines){
char buffer[1024];

send(fd, msg.c_str(), msg.length(), 0);
read(fd, buffer, 1024);
}

send(fd, (void*)"End Transfer", 1024, 0);

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🔴 send() buffer over-read for "End Transfer" string literal

send(fd, (void*)"End Transfer", 1024, 0) at server.cpp:55 transmits 1024 bytes from a 13-byte string literal, leaking program memory to the network peer.

Suggested change
send(fd, (void*)"End Transfer", 1024, 0);
send(fd, (void*)"End Transfer", strlen("End Transfer"), 0);
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Comment on lines +48 to +55

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🚩 Protocol mismatch: server sends msg.length() bytes but client expects null-terminated strings

In server.cpp:51, send(fd, msg.c_str(), msg.length(), 0) sends only the string contents without a null terminator. However, the client in kilo.c:1316-1317 does buffer[n] = '\0' then strcmp(buffer, "End Transfer"). Meanwhile the server's "End Transfer" sentinel at server.cpp:55 is sent with length 1024 (a separate bug), not strlen("End Transfer"). If the send length bugs are fixed to use actual string lengths, the protocol would need to be consistent about whether null terminators are included in the transmission. This is a fragile protocol design that will break in subtle ways depending on which bugs are fixed first.

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}
Comment on lines +34 to +56

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⚠️ Potential issue | 🔴 Critical

Critical: Buffer overread when sending transfer markers.

Lines 37 and 55 attempt to send 1024 bytes from string literals that are much shorter:

  • "Start Transfer" is 15 bytes (including null)
  • "End Transfer" is 13 bytes (including null)

This reads uninitialized memory beyond the string literals, which is undefined behavior.

🐛 Proposed fix
 void sendFile(int fd, vector<string> lines){
 	vector<string>::iterator i;
 
-	send(fd, (void*)"Start Transfer", 1024, 0);
+	send(fd, "Start Transfer", strlen("Start Transfer"), 0);
 
 	//this is the same as the loop that is commented out
 	for(string msg : lines){
 		char buffer[1024];
 
 		send(fd, msg.c_str(), msg.length(), 0);
 		read(fd, buffer, 1024);
 	}
 
-	send(fd, (void*)"End Transfer", 1024, 0);
+	send(fd, "End Transfer", strlen("End Transfer"), 0);
 }
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
void sendFile(int fd, vector<string> lines){
vector<string>::iterator i;
send(fd, (void*)"Start Transfer", 1024, 0);
/* for (i = lines.begin(); i != lines.end(); i++){
char buffer[1024];
string msg = *i;
// cout << "Line: " << msg << endl;
send(fd, msg.c_str(), msg.length(), 0);
read(fd, buffer, 1024);
} */
//this is the same as the loop that is commented out
for(string msg : lines){
char buffer[1024];
send(fd, msg.c_str(), msg.length(), 0);
read(fd, buffer, 1024);
}
send(fd, (void*)"End Transfer", 1024, 0);
}
void sendFile(int fd, vector<string> lines){
vector<string>::iterator i;
send(fd, "Start Transfer", strlen("Start Transfer"), 0);
/* for (i = lines.begin(); i != lines.end(); i++){
char buffer[1024];
string msg = *i;
// cout << "Line: " << msg << endl;
send(fd, msg.c_str(), msg.length(), 0);
read(fd, buffer, 1024);
} */
//this is the same as the loop that is commented out
for(string msg : lines){
char buffer[1024];
send(fd, msg.c_str(), msg.length(), 0);
read(fd, buffer, 1024);
}
send(fd, "End Transfer", strlen("End Transfer"), 0);
}
🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed.

In `@server.cpp` around lines 34 - 56, sendFile is calling send(fd, (void*)"Start
Transfer", 1024, 0) and send(fd, (void*)"End Transfer", 1024, 0), which reads
past the string literal and causes undefined behavior; change these calls to
send only the actual byte count (e.g., use strlen("Start Transfer") and
strlen("End Transfer") or use std::string and .size() / .c_str()) so you send
the exact length (optionally +1 if you need the terminating NUL), and keep the
rest of send/read logic in sendFile unchanged.


//threadFunc - thread function to read any messages from a client
void *threadFunc(void *args){
ssize_t n;
int clientFd = *(int*)args;
char buffer[1024];
pthread_detach(pthread_self());

// Read until disconnection
while ((n = read(clientFd, buffer, 1024)) > 0){
string line(buffer);
Comment on lines +66 to +67

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🔴 threadFunc constructs std::string from non-null-terminated buffer

At server.cpp:66-67, read(clientFd, buffer, 1024) does not null-terminate buffer. Then string line(buffer) constructs a string by scanning for a null terminator, reading past the actual data into uninitialized memory. This causes undefined behavior and incorrect command matching at lines 69/72.

Suggested change
while ((n = read(clientFd, buffer, 1024)) > 0){
string line(buffer);
while ((n = read(clientFd, buffer, 1023)) > 0){
buffer[n] = '\0';
string line(buffer);
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if (line == "exit"){
close(clientFd);
}
else if (line == "get"){
cout << "Get Received" << endl;
sendFile(clientFd, readFile());
}
}
return NULL;
}
Comment on lines +59 to +78

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⚠️ Potential issue | 🔴 Critical

Critical: Buffer not null-terminated and race condition on client file descriptor.

Two critical issues in the thread function:

  1. Missing null termination (Line 67): read() doesn't null-terminate the buffer, but string line(buffer) expects a null-terminated C-string. This reads garbage until a null byte is found.

  2. Race condition (Line 61): The clientFd is passed by pointer from main(), but main() reuses this local variable on the next accept() iteration. The thread may read a stale or incorrect file descriptor.

🐛 Proposed fix
 void *threadFunc(void *args){
 	ssize_t n;
-	int clientFd = *(int*)args;
+	int clientFd = (int)(intptr_t)args;  // Pass fd by value, not pointer
 	char buffer[1024];
 	pthread_detach(pthread_self());
 
 	// Read until disconnection
 	while ((n = read(clientFd, buffer, 1024)) > 0){
-		string line(buffer);
+		buffer[n] = '\0';  // Null-terminate the buffer
+		string line(buffer);
 		
 		if (line == "exit"){
 			close(clientFd);
+			return NULL;
 		}
 		else if (line == "get"){
 			cout << "Get Received" << endl;
 			sendFile(clientFd, readFile());	
 		}
 	}
+	close(clientFd);  // Close on disconnect
 	return NULL;
 }

And in main():

-		pthread_create(&thread, NULL, threadFunc, (void *)&clientFd);
+		pthread_create(&thread, NULL, threadFunc, (void *)(intptr_t)clientFd);
🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed.

In `@server.cpp` around lines 59 - 78, threadFunc currently constructs a
std::string from a non-null-terminated buffer and reads clientFd from a pointer
that the main thread reuses; fix by using the actual byte count returned by read
(use string line(buffer, n) or null-terminate buffer at buffer[n]=0) and avoid
the race by allocating the clientFd on the heap before creating the thread
(e.g., int* pclient = new int(clientFd) in main) and have threadFunc immediately
copy the value into a local int and delete/free the pointer (or otherwise claim
ownership) so the main thread can reuse its stack variable safely; ensure the
thread handles n==0/-1 correctly, closes the socket on "exit", and deletes/frees
the heap allocation before returning.


//handleSigInt - action performed when user types ctrl-C
void handleSigInt(int unused __attribute__((unused))){
exit(0);
}

//main server program
int main(void){

//setup SIGINT signal handler
signal(SIGINT, handleSigInt);

// Create server socket
int serverFd;
if ((serverFd = socket(AF_INET, SOCK_STREAM, 0)) < 0){
std::cerr << "Error: Can't create socket." << std::endl;
return 1;
}

// Set options for socket
int val;
if (setsockopt(serverFd, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(int))){
Comment on lines +99 to +100

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🔴 Uninitialized value passed to setsockopt for SO_REUSEADDR

At server.cpp:99-100, int val; is declared but never initialized, then passed to setsockopt(serverFd, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(int)). Using an uninitialized value is undefined behavior, and SO_REUSEADDR requires a non-zero value to be enabled. If val happens to be 0, the option won't take effect.

Suggested change
int val;
if (setsockopt(serverFd, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(int))){
int val = 1;
if (setsockopt(serverFd, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(int))){
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std::cerr << "Error: Can't reuse socket." << std::endl;
return 2;
}
Comment on lines +99 to +103

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⚠️ Potential issue | 🔴 Critical

Uninitialized variable passed to setsockopt().

The variable val is declared but never initialized before being passed to setsockopt(). For SO_REUSEADDR, it should be set to a non-zero value (typically 1) to enable the option.

🐛 Proposed fix
 	// Set options for socket
-	int val;
+	int val = 1;
 	if (setsockopt(serverFd, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(int))){
🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed.

In `@server.cpp` around lines 99 - 103, The variable `val` is used uninitialized
when calling setsockopt(serverFd, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(int));
initialize it to a non-zero value (typically 1) before the call and pass
sizeof(val) for clarity; i.e., set val = 1 prior to invoking setsockopt so
SO_REUSEADDR is actually enabled for serverFd.


// Configure addr and bind
struct sockaddr_in serverAddr;
serverAddr.sin_family = AF_INET;
serverAddr.sin_addr.s_addr = htonl(INADDR_ANY);
serverAddr.sin_port = htons(10001);
if (bind(serverFd, (struct sockaddr *)&serverAddr, sizeof(serverAddr)) == -1){
cerr << "Error: Can't bind socket to port." << endl;
return 3;
}

// Listen for client connections
if (listen(serverFd, 20) < 0){
cerr << "Error: Can't listen for clients." << endl;
return 4;
}

// Get name and port assigned to server
char *name = new char[1024];
struct sockaddr_in infoAddr;
socklen_t len = sizeof(infoAddr);
gethostname(name, 1024);
getsockname(serverFd, (struct sockaddr *)&infoAddr, &len);

// Report name and port
cout << name << ":" << ntohs(serverAddr.sin_port)<< endl;
delete name;

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🔴 delete used instead of delete[] for array allocation

At server.cpp:130, delete name is used to free memory allocated with new char[1024] at line 122. Using delete instead of delete[] for array allocations is undefined behavior.

Suggested change
delete name;
delete[] name;
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Comment on lines +122 to +130

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⚠️ Potential issue | 🟠 Major

Mismatched allocation/deallocation and unnecessary dynamic allocation.

Line 122 uses new char[1024] (array allocation) but line 130 uses delete name (scalar delete) instead of delete[] name. This is undefined behavior as flagged by static analysis.

Better yet, use a stack-allocated array since the size is fixed:

🔧 Proposed fix
 	// Get name and port assigned to server
-	char *name = new char[1024];
+	char name[1024];
 	struct sockaddr_in infoAddr;
 	socklen_t len = sizeof(infoAddr);
 	gethostname(name, 1024);
 	getsockname(serverFd, (struct sockaddr *)&infoAddr, &len);
 
 	// Report name and port
 	cout << name << ":" << ntohs(serverAddr.sin_port)<< endl;
-	delete name;
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
char *name = new char[1024];
struct sockaddr_in infoAddr;
socklen_t len = sizeof(infoAddr);
gethostname(name, 1024);
getsockname(serverFd, (struct sockaddr *)&infoAddr, &len);
// Report name and port
cout << name << ":" << ntohs(serverAddr.sin_port)<< endl;
delete name;
char name[1024];
struct sockaddr_in infoAddr;
socklen_t len = sizeof(infoAddr);
gethostname(name, 1024);
getsockname(serverFd, (struct sockaddr *)&infoAddr, &len);
// Report name and port
cout << name << ":" << ntohs(serverAddr.sin_port)<< endl;
🧰 Tools
🪛 Cppcheck (2.20.0)

[error] 130-130: Mismatching allocation and deallocation

(mismatchAllocDealloc)

🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed.

In `@server.cpp` around lines 122 - 130, The code allocates name with new
char[1024] but frees it with scalar delete and unnecessarily uses heap
allocation; replace the dynamic allocation with a stack buffer (e.g., declare
char name[1024]) and remove the delete, or if you must keep heap allocation use
delete[] name; locate the gethostname/getsockname usage around variables name,
serverFd and serverAddr and update the allocation/deallocation accordingly so
heap/stack usage is consistent and safe.


// Connect a client
struct sockaddr_in cliAddr;
len = sizeof(cliAddr);
while (true){
int clientFd = accept(serverFd, (struct sockaddr *)&serverAddr, &len);

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🔴 accept() overwrites serverAddr instead of writing to cliAddr

At server.cpp:136, accept(serverFd, (struct sockaddr *)&serverAddr, &len) passes &serverAddr (the server's address struct) instead of &cliAddr (declared at line 133 specifically to hold the client address). This overwrites the server's own address configuration with client information.

Suggested change
int clientFd = accept(serverFd, (struct sockaddr *)&serverAddr, &len);
int clientFd = accept(serverFd, (struct sockaddr *)&cliAddr, &len);
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⚠️ Potential issue | 🔴 Critical

Wrong sockaddr passed to accept().

Line 136 passes &serverAddr (the server's address) instead of &cliAddr (the client's address buffer). This corrupts the server's address structure and doesn't capture the client's address information.

🐛 Proposed fix
-		int clientFd = accept(serverFd, (struct sockaddr *)&serverAddr, &len);
+		int clientFd = accept(serverFd, (struct sockaddr *)&cliAddr, &len);
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
int clientFd = accept(serverFd, (struct sockaddr *)&serverAddr, &len);
int clientFd = accept(serverFd, (struct sockaddr *)&cliAddr, &len);
🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed.

In `@server.cpp` at line 136, The accept() call is passing the server's address
buffer (serverAddr) instead of the client's buffer (cliAddr), which corrupts
serverAddr and prevents capturing the peer address; update the accept invocation
that creates clientFd to pass (struct sockaddr *)&cliAddr (and ensure the length
variable `len` is the correct type like socklen_t and initialized) so the client
address is stored in `cliAddr` rather than overwriting `serverAddr`.


// Create thread to deal with client
pthread_t thread;
pthread_create(&thread, NULL, threadFunc, (void *)&clientFd);

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🔴 Race condition: address of loop-local clientFd passed to thread

At server.cpp:140, pthread_create(&thread, NULL, threadFunc, (void *)&clientFd) passes the address of the loop-local variable clientFd. On the next iteration, accept() at line 136 overwrites clientFd before the new thread may have had a chance to read it via *(int*)args at server.cpp:61. This causes multiple threads to potentially operate on the wrong file descriptor.

Prompt for agents
In server.cpp main(), the address of the loop-local variable clientFd is passed to the new thread via pthread_create at line 140. The next loop iteration's accept() call overwrites this variable before the thread may have copied it at server.cpp:61. Fix this by either: (1) heap-allocating an int for each client fd and having the thread free it, or (2) casting the int fd value directly to void* and back (e.g., (void*)(intptr_t)clientFd and (int)(intptr_t)args in threadFunc).
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}
return 0;
}
4 changes: 4 additions & 0 deletions test
Original file line number Diff line number Diff line change
@@ -0,0 +1,4 @@
this is a test file
these are some words
these are some more
bye!
Empty file added transfer
Empty file.