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fix(packetlen): read + calculate variable packet length

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This commit is contained in:
tyeth
2025-08-29 23:28:05 +01:00
parent 86669fd768
commit 7c81ab32c0
1 changed files with 14 additions and 94 deletions
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108
Adafruit_MQTT.cpp
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@@ -562,111 +562,31 @@ Adafruit_MQTT_Subscribe *Adafruit_MQTT::handleSubscriptionPacket(uint16_t len) {
return NULL;
}
// Parse out length of packet.
// NOTE: This includes data in the variable header and the payload.
Serial.print("Remaining len (len -4 header bytes): ");
uint16_t remainingLen = len - 4; // subtract the 4 header bytes
Serial.println(remainingLen);
uint16_t topicoffset = packetAdditionalLen(remainingLen);
Serial.print("Topic offset (packetAdditionalLen): ");
Serial.println(topicoffset);
uint16_t topicstart = topicoffset + 4;
Serial.print("Topic start (offset + 4): ");
Serial.println(topicstart);
Serial.print("buf[2 + topicoffset]: '");
Serial.print(buffer[2 + topicoffset]);
Serial.print("' (");
Serial.print(buffer[2 + topicoffset], HEX);
Serial.println(")");
uint16_t msb = buffer[2 + topicoffset] << 8;
Serial.print("MSB (buf[2 + topicoffset] << 8): ");
Serial.println(msb);
uint16_t lsb = buffer[3 + topicoffset];
Serial.print("LSB (buf[3 + topicoffset]): ");
Serial.print(lsb);
Serial.print(" ('");
Serial.print(buffer[3 + topicoffset]);
Serial.print("' = 0x");
Serial.print(buffer[3 + topicoffset], HEX);
Serial.println(")");
uint16_t topiclen_sb = int(msb | lsb);
Serial.print("Topic length (msb | lsb): ");
Serial.println(topiclen_sb);
topiclen = int((buffer[2 + topicoffset]) << 8 | buffer[3 + topicoffset]);
DEBUG_PRINT(F("Looking for subscription len "));
DEBUG_PRINTLN(topiclen);
// NEW WORKING CODE:
// Parse variable length encoding
// Parse MQTT Remaining Length field (variable length encoding).
// This field can be 1-4 bytes, so we must parse it byte-by-byte.
// Each byte uses the lower 7 bits for data, and the MSB as a continuation flag.
// This loop advances 'offset' to the first byte after the remaining length field.
uint32_t multiplier = 1;
DEBUG_PRINT("new technique - multiplier: 1");
uint32_t value = 0;
uint8_t encodedByte;
uint8_t offset = 1; // start after first header byte
uint8_t offset = 1; // Start after the fixed header byte
do {
encodedByte = buffer[offset++];
value += (encodedByte & 127) * multiplier;
multiplier *= 128;
// Infinite loop protection: MQTT spec allows max 4 bytes for this field
if (offset > 5) { // 1 (header) + 4 (max length bytes)
DEBUG_PRINTLN(F("Bad MQTT packet: Remaining Length field too long / malformed"));
return NULL;
}
} while ((encodedByte & 128) != 0);
DEBUG_PRINT(F("new technique - value: "));
DEBUG_PRINTLN(value);
DEBUG_PRINT(F("new technique - offset: "));
DEBUG_PRINTLN(offset);
// Now offset points to the first byte of topic length
// Now 'offset' points to the first byte of the topic length field.
// The topic length is always 2 bytes, big-endian.
uint16_t new_msb = buffer[offset] << 8;
DEBUG_PRINT(F("new technique - new_msb: "));
DEBUG_PRINTLN(new_msb);
uint16_t new_lsb = buffer[offset + 1];
DEBUG_PRINT(F("new technique - new_lsb: "));
DEBUG_PRINTLN(new_lsb);
uint16_t new_topiclen = new_msb | new_lsb;
DEBUG_PRINT(F("new technique - new_topiclen: "));
DEBUG_PRINTLN(new_topiclen);
uint16_t new_topicstart = offset + 2;
DEBUG_PRINT(F("new technique - new_topicstart: "));
DEBUG_PRINTLN(new_topicstart);
DEBUG_PRINT(F("Old topic offset (2 less) vs new topic offset: "));
DEBUG_PRINT(topicoffset);
DEBUG_PRINT(F(" vs "));
DEBUG_PRINTLN(new_topicstart);
DEBUG_PRINT(F("Old topic start vs new topic start: "));
DEBUG_PRINT(topicstart);
DEBUG_PRINT(F(" vs "));
DEBUG_PRINTLN(new_topicstart);
DEBUG_PRINT(F("Old topic len vs new topic len: "));
DEBUG_PRINT(topiclen);
DEBUG_PRINT(F(" vs "));
DEBUG_PRINTLN(new_topiclen);
topiclen = new_topiclen;
topicstart = new_topicstart;
/*
// Parse MQTT Remaining Length field (variable length encoding)
uint8_t headerLen = 1;
uint32_t remainingLen = 0;
uint8_t multiplier = 1;
uint8_t encodedByte;
do {
encodedByte = buffer[headerLen++];
remainingLen += (encodedByte & 127) * multiplier;
multiplier *= 128;
} while ((encodedByte & 128) != 0);
// Now headerLen is the offset to the variable header
uint16_t topiclen = (buffer[headerLen] << 8) | buffer[headerLen + 1];
const char* topic = (const char*)&buffer[headerLen + 2];
const uint8_t* payload = (const uint8_t*)&buffer[headerLen + 2 + topiclen];
// payload length = remainingLen - (2 + topiclen [+2 for packet id if QoS > 0])
*/
topiclen = new_msb | new_lsb;
uint16_t topicstart = offset + 2;
// Find subscription associated with this packet.
for (i = 0; i < MAXSUBSCRIPTIONS; i++) {