LibC: Implement strerror_r()

This implements the XSI-compliant version of strerror_r() - as opposed
to the GNU-specific variant.

The function explicitly saves errno so as to not accidentally change it
with one of the calls to other functions.

2 files changed, 21 insertions, 0 deletions

diff --git a/Userland/Libraries/LibC/string.cpp b/Userland/Libraries/LibC/string.cpp
index db74946ae8..3847afb6dc 100644
--- a/Userland/Libraries/LibC/string.cpp
+++ b/Userland/Libraries/LibC/string.cpp
@@ -354,6 +354,26 @@ const char* const sys_errlist[] = {
 
 int sys_nerr = EMAXERRNO;
 
+int strerror_r(int errnum, char* buf, size_t buflen)
+{
+    auto saved_errno = errno;
+    if (errnum >= EMAXERRNO) {
+        auto rc = strlcpy(buf, "unknown error", buflen);
+        if (rc >= buflen)
+            dbgln("strerror_r(): Invalid error number '{}' specified and the output buffer is too small.", errnum);
+        errno = saved_errno;
+        return EINVAL;
+    }
+    auto text = strerror(errnum);
+    auto rc = strlcpy(buf, text, buflen);
+    if (rc >= buflen) {
+        errno = saved_errno;
+        return ERANGE;
+    }
+    errno = saved_errno;
+    return 0;
+}
+
 char* strerror(int errnum)
 {
     if (errnum < 0 || errnum >= EMAXERRNO) {
diff --git a/Userland/Libraries/LibC/string.h b/Userland/Libraries/LibC/string.h
index beaf594a33..d7010ef6ac 100644
--- a/Userland/Libraries/LibC/string.h
+++ b/Userland/Libraries/LibC/string.h
@@ -43,6 +43,7 @@ char* strncat(char* dest, const char* src, size_t);
 
 size_t strspn(const char*, const char* accept);
 size_t strcspn(const char*, const char* reject);
+int strerror_r(int, char*, size_t);
 char* strerror(int errnum);
 char* strsignal(int signum);
 char* strpbrk(const char*, const char* accept);