From 06d92b3d25e02ace59f62b6d8411e63cbe125507 Mon Sep 17 00:00:00 2001
From: Camden Dixie O'Brien <cdo@wip.sh>
Date: Fri, 14 Oct 2022 11:24:39 +0100
Subject: [PATCH] Handle file requests

---
 main.c | 78 +++++++++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 72 insertions(+), 6 deletions(-)

diff --git a/main.c b/main.c
index a2933d8..077ada5 100644
--- a/main.c
+++ b/main.c
@@ -18,6 +18,7 @@
 
 #include <dirent.h>
 #include <errno.h>
+#include <fcntl.h>
 #include <netinet/in.h>
 #include <signal.h>
 #include <stdbool.h>
@@ -31,9 +32,13 @@
 #define HOST "::1"
 #define PORT 7070
 
+#define RESP_TERM ".\r\n"
+#define RESP_TERM_LEN 3 /* strlen(".\r\n") */
+
 #define PBUF_SIZE 1024
 #define RBUF_SIZE 1024
 #define SBUF_SIZE 1024
+#define FBUF_SIZE 1024
 
 /*
  * Enumeration of directory entry types.
@@ -87,7 +92,8 @@ int main(int argc, char *argv[])
 	(void)argv;
 
 	int res = EXIT_SUCCESS;
-	static char pbuf[PBUF_SIZE], rbuf[RBUF_SIZE], sbuf[SBUF_SIZE];
+	static char pbuf[PBUF_SIZE], rbuf[RBUF_SIZE], sbuf[SBUF_SIZE],
+	    fbuf[FBUF_SIZE];
 
 	/*
 	 * Get srvroot path from arguments and copy into pbuf.
@@ -211,7 +217,7 @@ int main(int argc, char *argv[])
 		/*
 		 * Construct the full path to the requested resource.
 		 *
-		 * This is needed in order to pass it to stat() and open() or
+		 * This is needed in order to pass it to stat() and fopen() or
 		 * opendir() later.  It must be null-terminated.  We also need
 		 * to make sure that none of the path's parts are "..", as
 		 * this could be used to escape the srvroot directory.
@@ -254,11 +260,71 @@ int main(int argc, char *argv[])
 		}
 		if (S_ISREG(rstat.st_mode)) {
 			/*
-			 * Send hard-coded response for files for now.
+			 * Open the file.
+			 *
+			 * The path is already null-terminated from the earlier call
+			 * to stat().
 			 */
-			const char *resp = "Files don't work yet\r\n.\r\n";
-			if (retrying_write(cfd, resp, strlen(resp)) == -1) {
-				fprintf(stderr, "Couldn't write to client socket\n");
+			FILE *rf;
+			do {
+				errno = 0;
+				rf = fopen(pbuf, "r");
+			} while (errno == EINTR);
+			if (rf == NULL) {
+				fprintf(stderr, "Failed to open %s\n", pbuf);
+				goto close_client_socket;
+			}
+
+			/*
+			 * Construct response in rbuf.
+			 *
+			 * The response should be the file contents, but with CRLF
+			 * line endings instead of just LF. Replacing the line
+			 * endings is done with a buffered reading approach to
+			 * minimize syscalls (as opposed to using fgetc()).
+			 */
+			unsigned rpos = 0;
+			while (true) {
+				/* Fill fbuf from file. */
+				n = fread(fbuf, sizeof(*fbuf), FBUF_SIZE, rf);
+				if (n != FBUF_SIZE && ferror(rf)) {
+					fprintf(stderr, "Failed to read from file %s\n", pbuf);
+					goto close_client_socket;
+				}
+
+				/* Copy from fbuf to rbuf, replacing LF with CRLF. */
+				for (unsigned fpos = 0; fpos < n; ++fpos) {
+					if (fbuf[fpos] == '\n') {
+						if (RBUF_SIZE - rpos < 2) {
+							fprintf(stderr, "Response buffer is too small");
+							goto close_client_socket;
+						}
+						rbuf[rpos++] = '\r';
+						rbuf[rpos++] = '\n';
+					} else {
+						if (RBUF_SIZE - rpos < 1) {
+							fprintf(stderr, "Response buffer is too small");
+							goto close_client_socket;
+						}
+						rbuf[rpos++] = fbuf[fpos];
+					}
+				}
+
+				if (feof(rf))
+					break;
+			}
+
+			/*
+			 * Terminate and send the response.
+			 */
+			if (RBUF_SIZE - rpos < RESP_TERM_LEN) {
+				fprintf(stderr, "Response buffer is too small");
+				goto close_client_socket;
+			}
+			memcpy(&rbuf[rpos], RESP_TERM, RESP_TERM_LEN);
+			rpos += RESP_TERM_LEN;
+			if (retrying_write(cfd, rbuf, rpos) == -1) {
+				fprintf(stderr, "Failed to write response to client\n");
 				goto close_client_socket;
 			}
 		} else if (S_ISDIR(rstat.st_mode)) {