Add support for metadata-only raw messages.

These messages contain only key-value metadata, no UAT message. They use a new output format beginning with '!' with no data section.
snstac · Feb 17, 2021 · a850dae · a850dae
1 parent cfdb31c
commit a850dae
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Showing 5 changed files with 54 additions and 6 deletions.
diff --git a/socket_input.cc b/socket_input.cc
@@ -178,12 +178,40 @@ static inline int hexvalue(char c) {
     }
 }
 
+boost::optional<RawMessage> RawInput::ParseMetadataLine(const std::string &line) {
+    // Parse metadata line that starts with '!'
+    RawMessage::MetadataMap metadata;
+
+    for (size_t i = 1; i < line.size();) {
+        auto equals = line.find('=', i);
+        auto semicolon = line.find(';', i);
+        if (equals == std::string::npos || semicolon == std::string::npos || semicolon < equals) {
+            // no more valid data
+            break;
+        }
+
+        auto key = line.substr(i, equals - i);
+        auto value = line.substr(equals + 1, semicolon - equals - 1);
+        metadata[key] = value;
+
+        i = semicolon + 1;
+    }
+
+    return RawMessage(std::move(metadata));
+}
+
 boost::optional<RawMessage> RawInput::ParseLine(const std::string &line) {
     if (line.size() < 2) {
         // too short
         return boost::none;
     }
 
+    if (line[0] == '!') {
+        // metadata only
+        return ParseMetadataLine(line);
+    }
+
+    // message with data payload
     if (line[0] != '-' && line[0] != '+') {
         // badly formatted
         return boost::none;

diff --git a/socket_input.h b/socket_input.h
@@ -36,6 +36,7 @@ namespace flightaware::uat {
         void ScheduleRead();
         void ParseBuffer();
         boost::optional<RawMessage> ParseLine(const std::string &line);
+        boost::optional<RawMessage> ParseMetadataLine(const std::string &line);
         void HandleError(const boost::system::error_code &ec);
 
         boost::asio::io_service &service_;

diff --git a/uat_message.cc b/uat_message.cc
@@ -28,16 +28,22 @@ std::ostream &flightaware::uat::operator<<(std::ostream &os, const RawMessage &m
     case MessageType::UPLINK:
         os << '+';
         break;
+    case MessageType::METADATA:
+        os << '!';
+        break;
     default:
         throw std::logic_error("unexpected message type");
     }
 
-    os << std::setfill('0');
-    for (auto b : message.Payload()) {
-        os << std::hex << std::setw(2) << (int)b;
+    if (message.Type() != MessageType::METADATA) {
+        os << std::setfill('0');
+        for (auto b : message.Payload()) {
+            os << std::hex << std::setw(2) << (int)b;
+        }
+
+        os << ";";
     }
 
-    os << ";";
     if (message.Errors() > 0) {
         os << "rs=" << std::dec << std::setw(0) << message.Errors() << ';';
     }
@@ -50,6 +56,10 @@ std::ostream &flightaware::uat::operator<<(std::ostream &os, const RawMessage &m
     if (message.RawTimestamp() != 0) {
         os << "rt=" << std::dec << std::setw(0) << message.RawTimestamp() << ';';
     }
+    for (auto &i : message.Metadata()) {
+        os << i.first << '=' << i.second << ';';
+    }
+
     return os;
 }
 

diff --git a/uat_message.h b/uat_message.h
@@ -20,7 +20,9 @@
 namespace flightaware::uat {
     class RawMessage {
       public:
-        RawMessage() : type_(MessageType::INVALID), received_at_(0), errors_(0), rssi_(0) {}
+        using MetadataMap = std::map<std::string, std::string>;
+
+        RawMessage() : type_(MessageType::INVALID), received_at_(0), errors_(0), rssi_(0), raw_timestamp_(0) {}
 
         RawMessage(const Bytes &payload, std::uint64_t received_at, unsigned errors, float rssi, std::uint64_t raw_timestamp = 0) : payload_(payload), received_at_(received_at), errors_(errors), rssi_(rssi), raw_timestamp_(raw_timestamp) {
             switch (payload_.size()) {
@@ -56,6 +58,10 @@ namespace flightaware::uat {
             }
         }
 
+        RawMessage(MetadataMap &&metadata) : type_(MessageType::METADATA), received_at_(0), errors_(0), rssi_(0.0), raw_timestamp_(0), metadata_(std::move(metadata)) {}
+
+        RawMessage(const MetadataMap &metadata) : type_(MessageType::METADATA), received_at_(0), errors_(0), rssi_(0.0), raw_timestamp_(0), metadata_(metadata) {}
+
         MessageType Type() const { return type_; }
 
         Bytes &Payload() { return payload_; }
@@ -70,6 +76,8 @@ namespace flightaware::uat {
 
         std::uint64_t RawTimestamp() const { return raw_timestamp_; }
 
+        const MetadataMap &Metadata() const { return metadata_; }
+
         // Number of raw bits in the message, excluding the sync bits
         unsigned BitLength() const {
             switch (type_) {
@@ -149,6 +157,7 @@ namespace flightaware::uat {
         unsigned errors_;
         float rssi_;
         std::uint64_t raw_timestamp_;
+        MetadataMap metadata_;
     };
 
     std::ostream &operator<<(std::ostream &os, const RawMessage &message);

diff --git a/uat_protocol.h b/uat_protocol.h
@@ -10,7 +10,7 @@
 #include <cstdint>
 
 namespace flightaware::uat {
-    enum class MessageType { DOWNLINK_SHORT, DOWNLINK_LONG, UPLINK, INVALID };
+    enum class MessageType { DOWNLINK_SHORT, DOWNLINK_LONG, UPLINK, METADATA, INVALID };
 
     const unsigned SYNC_BITS = 36;
     const std::uint64_t DOWNLINK_SYNC_WORD = 0xEACDDA4E2UL;