[hackers] [farbfeld] [PATCH] Improve fread error handling in ff2*

[Alexander Krotov]

In case of unexpected end of file errno is not set, and strerror(errno)
returns "Success". Caller should distinguish between error and EOF by
calling ferror(3) as described in fread(3).
---
 ff2jpg.c | 14 ++++++++++----
 ff2png.c |  7 +++++--
 ff2ppm.c | 14 ++++++++++----
 3 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/ff2jpg.c b/ff2jpg.c
index 3da35e2..6f88a23 100644
--- a/ff2jpg.c
+++ b/ff2jpg.c
@@ -80,8 +80,7 @@ main(int argc, char *argv[])
 
        /* header */
        if (fread(hdr, sizeof(*hdr), 4, stdin) != 4) {
-               fprintf(stderr, "%s: fread: %s\n", argv0, strerror(errno));
-               return 1;
+               goto readerr;
        }
        if (memcmp("farbfeld", hdr, sizeof("farbfeld") - 1)) {
                fprintf(stderr, "%s: invalid magic value\n", argv0);
@@ -124,8 +123,7 @@ main(int argc, char *argv[])
        /* write rows */
        for (i = 0; i < height; ++i) {
                if (fread(row, sizeof(uint16_t), rowlen, stdin) != rowlen) {
-                       fprintf(stderr, "%s: fread: %s\n", argv0, 
strerror(errno));
-                       return 1;
+                       goto readerr;
                }
                for (j = 0, k = 0; j < rowlen; j += 4, k += 3) {
                        a = ntohs(row[j + 3]);
@@ -142,4 +140,12 @@ main(int argc, char *argv[])
        jpeg_destroy_compress(&cinfo);
 
        return 0;
+readerr:
+       if (ferror(stdin)) {
+               fprintf(stderr, "%s: fread: %s\n", argv0, strerror(errno));
+       } else {
+               fprintf(stderr, "%s: unexpected end of file\n", argv0);
+       }
+
+       return 1;
 }
diff --git a/ff2png.c b/ff2png.c
index 4304bbb..5731082 100644
--- a/ff2png.c
+++ b/ff2png.c
@@ -81,8 +81,11 @@ main(int argc, char *argv[])
 
        return 0;
 readerr:
-       fprintf(stderr, "%s: fread: ", argv0);
-       perror(NULL);
+       if (ferror(stdin)) {
+               fprintf(stderr, "%s: fread: %s\n", argv0, strerror(errno));
+       } else {
+               fprintf(stderr, "%s: unexpected end of file\n", argv0);
+       }
 
        return 1;
 }
diff --git a/ff2ppm.c b/ff2ppm.c
index 880fa5b..2a67eb2 100644
--- a/ff2ppm.c
+++ b/ff2ppm.c
@@ -60,8 +60,7 @@ main(int argc, char *argv[])
 
        /* header */
        if (fread(hdr, sizeof(*hdr), 4, stdin) != 4) {
-               fprintf(stderr, "%s: fread: %s\n", argv0, strerror(errno));
-               return 1;
+               goto readerr;
        }
        if (memcmp("farbfeld", hdr, sizeof("farbfeld") - 1)) {
                fprintf(stderr, "%s: invalid magic value\n", argv0);
@@ -90,8 +89,7 @@ main(int argc, char *argv[])
        /* write rows */
        for (i = 0; i < height; ++i) {
                if (fread(row, sizeof(uint16_t), rowlen, stdin) != rowlen) {
-                       fprintf(stderr, "%s: fread: %s\n", argv0, 
strerror(errno));
-                       return 1;
+                       goto readerr;
                }
                for (j = 0, k = 0; j < rowlen; j += 4, k += 3) {
                        a = ntohs(row[j + 3]);
@@ -108,4 +106,12 @@ main(int argc, char *argv[])
        }
 
        return 0;
+readerr:
+       if (ferror(stdin)) {
+               fprintf(stderr, "%s: fread: %s\n", argv0, strerror(errno));
+       } else {
+               fprintf(stderr, "%s: unexpected end of file\n", argv0);
+       }
+
+       return 1;
 }
-- 
2.8.1