Apply warnings/suggestions reported by clang-tidy v9 (#67)

Clang-tidy version 9 reported a few warnings, and since we treat errors
as warnings we better address them.

I've disabled the trailing-return-type suggestion because I believe it's
ridiculous.

Signed-off-by: Marco Magdy <mmagdy@gmail.com>

.clang-tidy

@@ -1,5 +1,6 @@
 ---
-Checks:          'clang-diagnostic-*,clang-analyzer-*,performance-*,readability-*,modernize-*,bugprone-*,misc-*'
+Checks:
+'clang-diagnostic-*,clang-analyzer-*,performance-*,readability-*,modernize-*,bugprone-*,misc-*,-modernize-use-trailing-return-type'
 WarningsAsErrors: '*'
 HeaderFilterRegex: ''
 FormatStyle: 'none'
@@ -10,6 +11,7 @@ CheckOptions:
     value:           '1'
   - key:             readability-implicit-bool-conversion.AllowIntegerConditions
     value:           '1'
-
+  - key:             misc-non-private-member-variables-in-classes.IgnoreClassesWithAllMemberVariablesBeingPublic
+    value:           '1'
 
 ...

.gitignore

@@ -2,3 +2,4 @@ build
 tags
 TODO
 compile_commands.json
+.clangd

include/aws/lambda-runtime/outcome.h

@@ -15,6 +15,7 @@
  */
 
 #include <cassert>
+#include <utility>
 
 namespace aws {
 namespace lambda_runtime {
@@ -26,7 +27,7 @@ class outcome {
 
     outcome(TFailure const& f) : f(f), success(false) {}
 
-    outcome(outcome&& other) : success(other.success)
+    outcome(outcome&& other) noexcept : success(other.success)
     {
         if (success) {
             s = std::move(other.s);

src/logging.cpp

@@ -13,6 +13,7 @@
  * permissions and limitations under the License.
  */
 #include "aws/logging/logging.h"
+#include <array>
 #include <cstdio>
 #include <chrono>
 
@@ -46,9 +47,10 @@ void log(verbosity v, char const* tag, char const* msg, va_list args)
         va_end(copy);
         return;
     }
-    char buf[512];
-    char* out = buf;
-    if (sz >= static_cast<int>(sizeof(buf))) {
+    constexpr int max_stack_buffer_size = 512;
+    std::array<char, max_stack_buffer_size> buf;
+    char* out = buf.data();
+    if (sz >= max_stack_buffer_size) {
         out = new char[sz];
     }
 
@@ -60,7 +62,7 @@ void log(verbosity v, char const* tag, char const* msg, va_list args)
     // stdout is not line-buffered when redirected (for example to a file or to another process) so we must flush it
     // manually.
     fflush(stdout);
-    if (out != buf) {
+    if (out != buf.data()) {
         delete[] out;
     }
 }

src/runtime.cpp

@@ -33,13 +33,13 @@
 namespace aws {
 namespace lambda_runtime {
 
-static char const LOG_TAG[] = "LAMBDA_RUNTIME";
-static char const REQUEST_ID_HEADER[] = "lambda-runtime-aws-request-id";
-static char const TRACE_ID_HEADER[] = "lambda-runtime-trace-id";
-static char const CLIENT_CONTEXT_HEADER[] = "lambda-runtime-client-context";
-static char const COGNITO_IDENTITY_HEADER[] = "lambda-runtime-cognito-identity";
-static char const DEADLINE_MS_HEADER[] = "lambda-runtime-deadline-ms";
-static char const FUNCTION_ARN_HEADER[] = "lambda-runtime-invoked-function-arn";
+static constexpr auto LOG_TAG = "LAMBDA_RUNTIME";
+static constexpr auto REQUEST_ID_HEADER = "lambda-runtime-aws-request-id";
+static constexpr auto TRACE_ID_HEADER = "lambda-runtime-trace-id";
+static constexpr auto CLIENT_CONTEXT_HEADER = "lambda-runtime-client-context";
+static constexpr auto COGNITO_IDENTITY_HEADER = "lambda-runtime-cognito-identity";
+static constexpr auto DEADLINE_MS_HEADER = "lambda-runtime-deadline-ms";
+static constexpr auto FUNCTION_ARN_HEADER = "lambda-runtime-invoked-function-arn";
 
 enum Endpoints {
     INIT,
@@ -49,8 +49,10 @@ enum Endpoints {
 
 static bool is_success(aws::http::response_code httpcode)
 {
+    constexpr auto http_first_success_error_code = 200;
+    constexpr auto http_last_success_error_code = 299;
     auto const code = static_cast<int>(httpcode);
-    return code >= 200 && code <= 299;
+    return code >= http_first_success_error_code && code <= http_last_success_error_code;
 }
 
 static size_t write_data(char* ptr, size_t size, size_t nmemb, void* userdata)
@@ -67,13 +69,28 @@ static size_t write_data(char* ptr, size_t size, size_t nmemb, void* userdata)
     return nmemb;
 }
 
+// std::isspace has a few edge cases that would trigger UB. In particular, the documentation says:
+// "The behavior is undefined if the value of the input is not representable as unsigned char and is not equal to EOF."
+// So, this function does the simple obvious thing instead.
 static inline bool IsSpace(int ch)
 {
-    if (ch < -1 || ch > 255) {
-        return false;
+    constexpr int space = 0x20;           // space (0x20, ' ')
+    constexpr int form_feed = 0x0c;       // form feed (0x0c, '\f')
+    constexpr int line_feed = 0x0a;       // line feed (0x0a, '\n')
+    constexpr int carriage_return = 0x0d; // carriage return (0x0d, '\r')
+    constexpr int horizontal_tab = 0x09;  // horizontal tab (0x09, '\t')
+    constexpr int vertical_tab = 0x0b;    // vertical tab (0x0b, '\v')
+    switch (ch) {
+        case space:
+        case form_feed:
+        case line_feed:
+        case carriage_return:
+        case horizontal_tab:
+        case vertical_tab:
+            return true;
+        default:
+            return false;
     }
-
-    return ::isspace(ch) != 0;
 }
 
 static inline std::string trim(std::string s)
@@ -276,7 +293,8 @@ runtime::next_outcome runtime::get_next()
 
     if (resp.has_header(DEADLINE_MS_HEADER)) {
         auto const& deadline_string = resp.get_header(DEADLINE_MS_HEADER);
-        unsigned long ms = strtoul(deadline_string.c_str(), nullptr, 10);
+        constexpr int base = 10;
+        unsigned long ms = strtoul(deadline_string.c_str(), nullptr, base);
         assert(ms > 0);
         assert(ms < ULONG_MAX);
         req.deadline += std::chrono::milliseconds(ms);
@@ -437,10 +455,11 @@ void run_handler(std::function<invocation_response(invocation_request const&)> c
 
 static std::string json_escape(std::string const& in)
 {
+    constexpr char last_non_printable_character = 31;
     std::string out;
     out.reserve(in.length()); // most strings will end up identical
     for (char ch : in) {
-        if (ch > 31 && ch != '\"' && ch != '\\') {
+        if (ch > last_non_printable_character && ch != '\"' && ch != '\\') {
             out.append(1, ch);
         }
         else {
@@ -469,9 +488,10 @@ static std::string json_escape(std::string const& in)
                     break;
                 default:
                     // escape and print as unicode codepoint
-                    char buf[6]; // 4 hex + letter 'u' + \0
-                    sprintf(buf, "u%04x", ch);
-                    out.append(buf, 5); // add only five, discarding the null terminator.
+                    constexpr int printed_unicode_length = 6; // 4 hex + letter 'u' + \0
+                    std::array<char, printed_unicode_length> buf;
+                    sprintf(buf.data(), "u%04x", ch);
+                    out.append(buf.data(), buf.size() - 1); // add only five, discarding the null terminator.
                     break;
             }
         }