Compute and store message sha256 on send

[markmnl]

Import github.com/markmnl/fmsgd/pkg/fmsg and use it in the Send handler to build the wire-format fmsg.Header from in-memory fields, then call GetMessageHash() to obtain the SHA-256 over the encoded header + decompressed body + attachment data. The hash is written to msg.sha256 in the same UPDATE that sets time_sent.

Also update fetchMessage to SELECT add_to_from so the Send handler has the correct AddToFrom value when building the header for add-to messages.

This fixes the production error where POST /fmsg with a pid failed because the parent message had sha256 = NULL and the DB trigger populate_msg_psha256_from_pid requires a non-null sha256 on any sent parent message.

[Copilot]

Pull request overview

This PR updates the message send flow to compute and persist a deterministic SHA-256 hash for a message at send-time, using the canonical fmsg wire-format header/body/attachments encoding, and ensures add_to_from is available when constructing the header.

Changes:

• Import github.com/markmnl/fmsgd/pkg/fmsg and compute msg.sha256 during POST /fmsg/:id/send in the same DB update that sets time_sent.
• Load additional DB fields needed for hash computation (add_to_from, psha256, and attachment header metadata).
• Add the github.com/markmnl/fmsgd module dependency.

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/handlers/messages.go	Compute and store message sha256 on send; extend fetchMessage to select add_to_from.
src/go.mod	Adds the github.com/markmnl/fmsgd module requirement.
src/go.sum	Adds checksums for the newly required github.com/markmnl/fmsgd module.

Comments suppressed due to low confidence (2)

src/handlers/messages.go:857

• Attachment metadata is loaded with errors silently ignored (attErr ignored, per-row Scan errors ignored, and attRows.Err() is never checked). If any scan/query issue occurs, the hash may be computed without some attachments and then written to msg.sha256, permanently diverging from the real wire-format hash. Please fail the request if attachment metadata cannot be read completely/correctly.

	attRows, attErr := h.DB.Pool.Query(ctx,
		"SELECT flags, type, filename, filesize, filepath FROM msg_attachment WHERE msg_id = $1 ORDER BY position",
		msgID,
	)
	if attErr == nil {
		for attRows.Next() {
			var a attachMeta
			if scanErr := attRows.Scan(&a.flags, &a.typ, &a.filename, &a.filesize, &a.path); scanErr == nil {
				attachments = append(attachments, a)
			}
		}
		attRows.Close()
	}

src/handlers/messages.go:843

• attachMeta.filesize is declared as int32, but attachments are written with an int64 byte count (io.Copy result) and DB filesize is likely a 64-bit integer. If a value is out of int32 range, pgx will return a scan error (currently ignored) and the attachment will be omitted from the hash. Use int64 for scanning and validate it fits into the wire/header size type before casting.

	type attachMeta struct {
		flags    int16
		typ      string
		filename string
		filesize int32
		path     string
	}

[markmnl]

@copilot apply changes based on this feedback

[Copilot]

Fixed in commit 18ccd92:

• psha256 lookup now uses err = instead of _ =, returning 5xx on any DB error
• Added a length check: if psha256 is not exactly 32 bytes, the handler returns 5xx with a clear error message
• Attachment query errors now return 5xx instead of silently treating it as "no attachments"
• Per-row scan errors during attachment iteration now close the rows and return 5xx
• Added attRows.Err() check after the iteration loop