Firebase Storage: Allowing metadata to be cleared (#197)

* Allowing metadata to be cleared

3 files changed, 57 insertions, 2 deletions

diff --git a/Firebase/Storage/FIRStorageMetadata.m b/Firebase/Storage/FIRStorageMetadata.m
index 4269a45..c4ff5a8 100644
--- a/Firebase/Storage/FIRStorageMetadata.m
+++ b/Firebase/Storage/FIRStorageMetadata.m
@@ -31,6 +31,8 @@
 - (instancetype)initWithDictionary:(NSDictionary *)dictionary {
   self = [super init];
   if (self) {
+    _initialMetadata = [dictionary copy];
+
     _bucket = dictionary[kFIRStorageMetadataBucket];
     _cacheControl = dictionary[kFIRStorageMetadataCacheControl];
     _contentDisposition = dictionary[kFIRStorageMetadataContentDisposition];
@@ -73,7 +75,10 @@
 #pragma mark - NSObject overrides
 
 - (instancetype)copyWithZone:(NSZone *)zone {
-  return [[[self class] allocWithZone:zone] initWithDictionary:[self dictionaryRepresentation]];
+  FIRStorageMetadata *clone =
+      [[[self class] allocWithZone:zone] initWithDictionary:[self dictionaryRepresentation]];
+  clone.initialMetadata = [self.initialMetadata copy];
+  return clone;
 }
 
 - (BOOL)isEqual:(id)object {
@@ -200,6 +205,36 @@
   return [_downloadURLs firstObject];
 }
 
+#pragma mark - Private methods
+
++ (void)removeMatchingMetadata:(NSMutableDictionary *)metadata
+                   oldMetadata:(NSDictionary *)oldMetadata {
+  for (NSString* metadataKey in [oldMetadata allKeys]) {
+    id oldValue = [oldMetadata objectForKey:metadataKey];
+    id newValue = [metadata objectForKey:metadataKey];
+
+    if (oldValue && !newValue) {
+      [metadata setObject:[NSNull null] forKey:metadataKey];
+    } else if ([oldValue isKindOfClass:[NSString class]] &&
+               [newValue isKindOfClass:[NSString class]]) {
+      if ([oldValue isEqualToString:newValue]) {
+        [metadata removeObjectForKey:metadataKey];
+      }
+    } else if ([oldValue isKindOfClass:[NSDictionary class]] &&
+               [newValue isKindOfClass:[NSDictionary class]]) {
+      NSMutableDictionary *nestedMetadata = [newValue mutableCopy];
+      [self removeMatchingMetadata:nestedMetadata oldMetadata:oldValue];
+      [metadata setObject:[nestedMetadata copy] forKey:metadataKey];
+    }
+  }
+}
+
+- (NSDictionary *)updatedMetadata {
+  NSMutableDictionary *metadataUpdate = [[self dictionaryRepresentation] mutableCopy];
+  [FIRStorageMetadata removeMatchingMetadata:metadataUpdate oldMetadata:_initialMetadata];
+  return [metadataUpdate copy];
+}
+
 #pragma mark - RFC 3339 conversions
 
 static NSDateFormatter *sRFC3339DateFormatter;
diff --git a/Firebase/Storage/FIRStorageUpdateMetadataTask.m b/Firebase/Storage/FIRStorageUpdateMetadataTask.m
index 005f78f..642ebcd 100644
--- a/Firebase/Storage/FIRStorageUpdateMetadataTask.m
+++ b/Firebase/Storage/FIRStorageUpdateMetadataTask.m
@@ -45,7 +45,7 @@
 
 - (void)enqueue {
   NSMutableURLRequest *request = [self.baseRequest mutableCopy];
-  NSDictionary *updateDictionary = [_updateMetadata dictionaryRepresentation];
+  NSDictionary *updateDictionary = [_updateMetadata updatedMetadata];
   NSData *updateData = [NSData frs_dataFromJSONDictionary:updateDictionary];
   request.HTTPMethod = @"PATCH";
   request.timeoutInterval = self.reference.storage.maxUploadRetryTime;
diff --git a/Firebase/Storage/Private/FIRStorageMetadata_Private.h b/Firebase/Storage/Private/FIRStorageMetadata_Private.h
index 629c935..ad8cc94 100644
--- a/Firebase/Storage/Private/FIRStorageMetadata_Private.h
+++ b/Firebase/Storage/Private/FIRStorageMetadata_Private.h
@@ -15,6 +15,7 @@
  */
 
 #import "FIRStorageConstants_Private.h"
+#import "FIRStorageMetadata.h"
 
 @class FIRStorageReference;
 
@@ -34,6 +35,25 @@ NS_ASSUME_NONNULL_BEGIN
 @property(readwrite) FIRStorageMetadataType type;
 
 /**
+ * The original metadata representation received from the server or an empty dictionary
+ * if the metadata object was initialized by the user.
+ */
+@property(copy, nonatomic) NSDictionary *initialMetadata;
+
+/**
+ * Recursively removes entries in 'metadata' that are unmodified from 'oldMetadata'.
+ * Adds 'NSNull' for entries that only exist in oldMetadata.
+ */
++ (void)removeMatchingMetadata:(NSMutableDictionary *)metadata
+                   oldMetadata:(NSDictionary *)oldMetadata;
+
+/**
+ * Computes the updates between the state at initialization and the current state.
+ * Returns a dictionary with only the updated data. Removed keys are set to NSNull.
+ */
+- (NSDictionary *)updatedMetadata;
+
+/**
  * Returns an RFC3339 formatted date from a string.
  * @param dateString An NSString of the form: yyyy-MM-ddTHH:mm:ss.SSSZ.
  * @return An NSDate populated from the string or nil if conversion isn't possible.