Make strlcpy available in folly, second attempt

Summary: strncpy is bad.  strlcpy is somewhat less bad.  We already had
this function, but let's move it somewhere more reasonable.

This would make sense to live in String.h, but then we have circular
dependencies.  Since String.h includes Demangle.h, though, you get
strlcpy by including it, so this should be okay enough.

Reviewed By: @lbrandy

Differential Revision: D2097590

folly/Demangle.cpp

@@ -55,21 +55,6 @@ extern "C" int cplus_demangle_v3_callback(
 
 #endif
 
-namespace {
-
-// glibc doesn't have strlcpy
-size_t my_strlcpy(char* dest, const char* src, size_t size) {
-  size_t len = strlen(src);
-  if (size != 0) {
-    size_t n = std::min(len, size - 1);  // always null terminate!
-    memcpy(dest, src, n);
-    dest[n] = '\0';
-  }
-  return len;
-}
-
-}  // namespace
-
 namespace folly {
 
 #if FOLLY_HAVE_CPLUS_DEMANGLE_V3_CALLBACK
@@ -106,6 +91,16 @@ void demangleCallback(const char* str, size_t size, void* p) {
 
 }  // namespace
 
+size_t strlcpy(char* dest, const char* const src, size_t size) {
+  size_t len = strlen(src);
+  if (size != 0) {
+    size_t n = std::min(len, size - 1);  // always null terminate!
+    memcpy(dest, src, n);
+    dest[n] = '\0';
+  }
+  return len;
+}
+
 size_t demangle(const char* name, char* out, size_t outSize) {
   DemangleBuf dbuf;
   dbuf.dest = out;
@@ -119,7 +114,7 @@ size_t demangle(const char* name, char* out, size_t outSize) {
       demangleCallback,
       &dbuf);
   if (status == 0) {  // failed, return original
-    return my_strlcpy(out, name, outSize);
+    return folly::strlcpy(out, name, outSize);
   }
   if (outSize != 0) {
     *dbuf.dest = '\0';
@@ -134,7 +129,7 @@ fbstring demangle(const char* name) {
 }
 
 size_t demangle(const char* name, char* out, size_t outSize) {
-  return my_strlcpy(out, name, outSize);
+  return folly::strlcpy(out, name, outSize);
 }
 
 #endif

folly/Demangle.h

@@ -59,4 +59,7 @@ inline size_t demangle(const std::type_info& type, char* buf, size_t bufSize) {
   return demangle(type.name(), buf, bufSize);
 }
 
+// glibc doesn't have strlcpy
+size_t strlcpy(char* dest, const char* const src, size_t size);
+
 }

folly/test/DemangleTest.cpp

@@ -48,6 +48,28 @@ TEST(Demangle, demangle) {
 }
 #endif
 
+TEST(Demangle, strlcpy) {
+  char buf[6];
+
+  EXPECT_EQ(3, folly::strlcpy(buf, "abc", 6));
+  EXPECT_EQ('\0', buf[3]);
+  EXPECT_EQ("abc", std::string(buf));
+
+  EXPECT_EQ(7, folly::strlcpy(buf, "abcdefg", 3));
+  EXPECT_EQ('\0', buf[2]);
+  EXPECT_EQ("ab", std::string(buf));
+
+  const char* big_string = "abcdefghijklmnop";
+
+  EXPECT_EQ(strlen(big_string), folly::strlcpy(buf, big_string, sizeof(buf)));
+  EXPECT_EQ('\0', buf[5]);
+  EXPECT_EQ("abcde", std::string(buf));
+
+  buf[0] = 'z';
+  EXPECT_EQ(strlen(big_string), folly::strlcpy(buf, big_string, 0));
+  EXPECT_EQ('z', buf[0]);  // unchanged, size = 0
+}
+
 int main(int argc, char *argv[]) {
   testing::InitGoogleTest(&argc, argv);
   gflags::ParseCommandLineFlags(&argc, &argv, true);