From 51f312aa5777f380abd2d100212317f249cd7f2c Mon Sep 17 00:00:00 2001
From: Gregory Oschwald <goschwald@maxmind.com>
Date: Sun, 18 Aug 2024 16:09:18 -0700
Subject: [PATCH] Remove (*Reader).Decode

And replace it with (*Reader).LookupOffset
---
 reader.go      | 24 +++++-------------------
 reader_test.go | 17 +++++++++++------
 2 files changed, 16 insertions(+), 25 deletions(-)

diff --git a/reader.go b/reader.go
index e9f76c3..c52dedc 100644
--- a/reader.go
+++ b/reader.go
@@ -150,28 +150,14 @@ func (r *Reader) Lookup(ip netip.Addr) Result {
 	}
 }
 
-// Decode the record at |offset| into |result|. The result value pointed to
-// must be a data value that corresponds to a record in the database. This may
-// include a struct representation of the data, a map capable of holding the
-// data or an empty any value.
-//
-// If result is a pointer to a struct, the struct need not include a field
-// for every value that may be in the database. If a field is not present in
-// the structure, the decoder will not decode that field, reducing the time
-// required to decode the record.
-//
-// As a special case, a struct field of type uintptr will be used to capture
-// the offset of the value. Decode may later be used to extract the stored
-// value from the offset. MaxMind DBs are highly normalized: for example in
-// the City database, all records of the same country will reference a
-// single representative record for that country. This uintptr behavior allows
-// clients to leverage this normalization in their own sub-record caching.
-func (r *Reader) Decode(offset uintptr, result any) error {
+// LookupOffset returns the Result for the specified offset. Note that
+// netip.Prefix returned by Networks will be invalid when using LookupOffset.
+func (r *Reader) LookupOffset(offset uintptr) Result {
 	if r.buffer == nil {
-		return errors.New("cannot call Decode on a closed database")
+		return Result{err: errors.New("cannot call Decode on a closed database")}
 	}
 
-	return Result{decoder: r.decoder, offset: uint(offset)}.Decode(result)
+	return Result{decoder: r.decoder, offset: uint(offset)}
 }
 
 var zeroIP = netip.MustParseAddr("::")
diff --git a/reader_test.go b/reader_test.go
index 3976b84..968bbdd 100644
--- a/reader_test.go
+++ b/reader_test.go
@@ -311,7 +311,8 @@ func TestDecoder(t *testing.T) {
 		require.NoError(t, result.Err())
 		require.True(t, result.Found())
 
-		require.NoError(t, reader.Decode(result.RecordOffset(), &testV))
+		res := reader.LookupOffset(result.RecordOffset())
+		require.NoError(t, res.Decode(&testV))
 		verify(testV)
 	}
 
@@ -563,21 +564,25 @@ func TestNestedOffsetDecode(t *testing.T) {
 			TimeZoneOffset uintptr `maxminddb:"time_zone"`
 		} `maxminddb:"location"`
 	}
-	require.NoError(t, db.Decode(result.RecordOffset(), &root))
+	res := db.LookupOffset(result.RecordOffset())
+	require.NoError(t, res.Decode(&root))
 	assert.InEpsilon(t, 51.5142, root.Location.Latitude, 1e-10)
 
 	var longitude float64
-	require.NoError(t, db.Decode(root.Location.LongitudeOffset, &longitude))
+	res = db.LookupOffset(root.Location.LongitudeOffset)
+	require.NoError(t, res.Decode(&longitude))
 	assert.InEpsilon(t, -0.0931, longitude, 1e-10)
 
 	var timeZone string
-	require.NoError(t, db.Decode(root.Location.TimeZoneOffset, &timeZone))
+	res = db.LookupOffset(root.Location.TimeZoneOffset)
+	require.NoError(t, res.Decode(&timeZone))
 	assert.Equal(t, "Europe/London", timeZone)
 
 	var country struct {
 		IsoCode string `maxminddb:"iso_code"`
 	}
-	require.NoError(t, db.Decode(root.CountryOffset, &country))
+	res = db.LookupOffset(root.CountryOffset)
+	require.NoError(t, res.Decode(&country))
 	assert.Equal(t, "GB", country.IsoCode)
 
 	require.NoError(t, db.Close())
@@ -680,7 +685,7 @@ func TestUsingClosedDatabase(t *testing.T) {
 	err = reader.Lookup(addr).Decode(recordInterface)
 	assert.Equal(t, "cannot call Lookup on a closed database", err.Error())
 
-	err = reader.Decode(0, recordInterface)
+	err = reader.LookupOffset(0).Decode(recordInterface)
 	assert.Equal(t, "cannot call Decode on a closed database", err.Error())
 }