Fix format detection: check file content for PGDMP signature, not just extension

internal/restore/formats.go

@@ -1,6 +1,9 @@
 package restore
 
 import (
+	"compress/gzip"
+	"io"
+	"os"
 	"strings"
 )
 
@@ -18,7 +21,7 @@ const (
 	FormatUnknown          ArchiveFormat = "Unknown"
 )
 
-// DetectArchiveFormat detects the format of a backup archive from its filename
+// DetectArchiveFormat detects the format of a backup archive from its filename and content
 func DetectArchiveFormat(filename string) ArchiveFormat {
 	lower := strings.ToLower(filename)
 
@@ -27,11 +30,24 @@ func DetectArchiveFormat(filename string) ArchiveFormat {
 		return FormatClusterTarGz
 	}
 
-	// Check for compressed formats
+	// For .dump files, check if they're actually custom format or SQL text
 	if strings.HasSuffix(lower, ".dump.gz") {
-		return FormatPostgreSQLDumpGz
+		if isCustomFormat(filename, true) {
+			return FormatPostgreSQLDumpGz
+		}
+		// If not custom format, treat as SQL
+		return FormatPostgreSQLSQLGz
 	}
 
+	if strings.HasSuffix(lower, ".dump") {
+		if isCustomFormat(filename, false) {
+			return FormatPostgreSQLDump
+		}
+		// If not custom format, treat as SQL
+		return FormatPostgreSQLSQL
+	}
+
+	// Check for compressed SQL formats
 	if strings.HasSuffix(lower, ".sql.gz") {
 		// Determine if MySQL or PostgreSQL based on naming convention
 		if strings.Contains(lower, "mysql") || strings.Contains(lower, "mariadb") {
@@ -40,11 +56,7 @@ func DetectArchiveFormat(filename string) ArchiveFormat {
 		return FormatPostgreSQLSQLGz
 	}
 
-	// Check for uncompressed formats
+	// Check for uncompressed SQL formats
-	if strings.HasSuffix(lower, ".dump") {
-		return FormatPostgreSQLDump
-	}
-
 	if strings.HasSuffix(lower, ".sql") {
 		// Determine if MySQL or PostgreSQL based on naming convention
 		if strings.Contains(lower, "mysql") || strings.Contains(lower, "mariadb") {
@@ -60,6 +72,36 @@ func DetectArchiveFormat(filename string) ArchiveFormat {
 	return FormatUnknown
 }
 
+// isCustomFormat checks if a file is PostgreSQL custom format (has PGDMP signature)
+func isCustomFormat(filename string, compressed bool) bool {
+	file, err := os.Open(filename)
+	if err != nil {
+		return false
+	}
+	defer file.Close()
+
+	var reader io.Reader = file
+
+	// Handle compression
+	if compressed {
+		gz, err := gzip.NewReader(file)
+		if err != nil {
+			return false
+		}
+		defer gz.Close()
+		reader = gz
+	}
+
+	// Read first 5 bytes to check for PGDMP signature
+	buffer := make([]byte, 5)
+	n, err := reader.Read(buffer)
+	if err != nil || n < 5 {
+		return false
+	}
+
+	return string(buffer) == "PGDMP"
+}
+
 // IsCompressed returns true if the archive format is compressed
 func (f ArchiveFormat) IsCompressed() bool {
 	return f == FormatPostgreSQLDumpGz ||