mx_util: Add mx_read_first_line_from_file()

mx_util.c

@@ -752,6 +752,34 @@ int mx_open_newfile(char *fname)
     return fh;
 }
 
+int mx_read_first_line_from_file(char *fname, char **line)
+{
+    _mx_cleanup_fclose_ FILE *fp;
+    char *buf = NULL;
+    size_t n = 0;
+    ssize_t res;
+
+    fp = fopen(fname, "r");
+    if (!fp)
+        return -errno;
+
+    res = getline(&buf, &n, fp);
+    if (res == -1)
+        return -errno;
+
+    *line = buf;
+
+    if (!res)
+        return res;
+
+    res--;
+
+    if (buf[res] == '\n')
+        buf[res] = 0;
+
+    return res;
+}
+
 int mx_sleep(unsigned int seconds)
 {
     if (seconds)

mx_util.h

@@ -5,6 +5,7 @@
 #include <stdint.h>
 #include <stdarg.h>
 #include <string.h>
+#include <stdio.h>
 
 #include "mx_log.h"
 
@@ -46,9 +47,17 @@ static inline void __mx_free(void *ptr) {
     free(*(void **)ptr);
 }
 
+static inline void __mx_fclose(FILE **ptr) {
+    if (*ptr)
+        fclose(*ptr);
+}
+
 #undef _mx_cleanup_free_
 #define _mx_cleanup_free_ _mx_cleanup_(__mx_free)
 
+#undef _mx_cleanup_fclose_
+#define _mx_cleanup_fclose_ _mx_cleanup_(__mx_fclose)
+
 #undef likely
 #define likely(x)       __builtin_expect((x),1)
 
@@ -106,6 +115,8 @@ int mx_setenvf_forever(const char *name, char *fmt, ...) __attribute__ ((format(
 
 int mx_open_newfile(char *fname);
 
+int mx_read_first_line_from_file(char *fname, char **line);
+
 int mx_sleep(unsigned int seconds);
 int mx_sleep_nofail(unsigned int seconds);
 

test_mx_util.c

@@ -44,6 +44,7 @@ static void test_mx_strtoul(void)
     assert(mx_strtoul("-1", &l) == -ERANGE);
     assert(mx_strtoul(" -1", &l) == -ERANGE);
 
+    assert(mx_strtoul("123 123", &l) == -EINVAL);
     assert(mx_strtoul("123s", &l) == -EINVAL);
     assert(mx_strtoul("0888", &l) == -EINVAL);
     assert(mx_strtoul("1.2", &l)  == -EINVAL);
@@ -271,6 +272,26 @@ static void test_mx_strtobytes(void)
     assert(mx_strtobytes("test", &l) == -EINVAL);
 }
 
+static void test_mx_read_first_line_from_file(void)
+{
+    char *str;
+
+    assert(mx_read_first_line_from_file("/proc/sys/kernel/random/boot_id", &str) == 36);
+    assert(str);
+    mx_free_null(str);
+
+    assert(mx_read_first_line_from_file("/proc/sys/kernel/random/uuid", &str) == 36);
+    assert(str);
+    mx_free_null(str);
+
+    assert(mx_read_first_line_from_file("/proc/no_such_file", &str) == -ENOENT);
+    assert(str == NULL);
+
+    assert(mx_read_first_line_from_file("/proc/self/stat", &str) > 0);
+    assert(str);
+    mx_free_null(str);
+}
+
 int main(int argc, char *argv[])
 {
     test_mx_strskipwhitespaces();
@@ -284,5 +305,6 @@ int main(int argc, char *argv[])
     test_mx_strtoseconds();
     test_mx_strtominutes();
     test_mx_strtobytes();
+    test_mx_read_first_line_from_file();
     return 0;
 }