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JuliaLang · Feb 1, 2023 · a30270e · a30270e
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diff --git a/README.md b/README.md
@@ -14,11 +14,13 @@ Julia 1.3 through 1.5 as well.
 
 ## API
 
-The public API of `Downloads` consists of three functions and three types:
+The public API of `Downloads` consists of the following functions and types:
 
 - `download` — download a file from a URL, erroring if it can't be downloaded
 - `request` — request a URL, returning a `Response` object indicating success
 - `default_downloader!` - set the default `Downloader` object
+- `pushhook!` — add a hook which allows for customizing downloading parameters
+- `deletehook!` — remove a previously added parameter customization hook
 - `Response` — a type capturing the status and other metadata about a request
 - `RequestError` — an error type thrown by `download` and `request` on error
 - `Downloader` — an object encapsulating shared resources for downloading
@@ -141,6 +143,52 @@ with getting a response at all, then a `RequestError` is thrown or returned.
 Set the default `Downloader`. If no argument is provided, resets the default downloader 
 so that a fresh one is created the next time the default downloader is needed.
 
+### pushhook!
+```jl
+    pushhook!(hook) -> key
+```
+- `hook       :: Function`
+- `key        :: HookKey`
+
+Add a hook to customize download parameters for all downloads.  
+
+The signature `hook` should be `(easy::Easy, info::Dict) -> Nothing`. 
+Multiple hooks can be added with repeated calls to `pushhook!`.  Hooks are 
+applied in the order they were added. 
+
+The returned `key` maybe used to remove a previously added `hook` cf. `deletehook!`
+
+Examples:
+```jl
+# define hook
+hook = (easy, info) -> begin
+    # allow for long pauses during downloads 
+    # (perhaps for malware scanning)
+    setopt(easy, Downloads.Curl.CURLOPT_LOW_SPEED_LIMIT, 1   #= bytes   =#)
+    setopt(easy, Downloads.Curl.CURLOPT_LOW_SPEED_TIME , 200 #= seconds =#)
+    # other possibilities
+      # set ca_roots
+      # disable certificate verification
+      # block or rewrite URLs
+end
+
+# add hook
+key = pushhook!(hook)
+
+# would fail with default download parameters...
+download("https://httpbingo.julialang.org/delay/40", "test.txt")
+
+# cleanup
+deletehook!(key)
+```
+
+### deletehook!
+```jl
+    deletehook!(key) 
+```
+- `key        :: HookKey`
+
+Remove a hook previously added with `pushhook!.
 ### Response
 
 ```jl

diff --git a/src/Downloads.jl b/src/Downloads.jl
@@ -7,6 +7,8 @@ More generally, the module exports functions and types that provide lower-level
 for file downloading:
 - [`download`](@ref) — download a file from a URL, erroring if it can't be downloaded
 - [`request`](@ref) — request a URL, returning a `Response` object indicating success
+- [`pushhook!`](@ref) — add a hook which allows for customizing downloading parameters
+- [`deletehook!`](@ref) — remove a previously added parameter customization hook
 - [`Response`](@ref) — a type capturing the status and other metadata about a request
 - [`RequestError`](@ref) — an error type thrown by `download` and `request` on error
 - [`Downloader`](@ref) — an object encapsulating shared resources for downloading
@@ -77,30 +79,75 @@ const EASY_HOOK = Ref{Union{Function, Nothing}}(nothing)
 ## Allow for a set of global hooks that can customize each download (via setting parameters on the 
 ## `Easy` object associated with a request 
 const HookKey = Int
-current_key = 0
+CURRENT_KEY = 0
 GlobalHookEntry = Tuple{HookKey, Function}
 const GLOBAL_HOOK_LOCK = ReentrantLock() 
 const GLOBAL_HOOKS = Array{GlobalHookEntry,1}(undef, 0)
 
 ## Add hook
+"""
+    pushhook!(hook) -> key
+
+    hook       :: Function
+    key        :: HookKey
+Add a hook to customize download parameters for all downloads.  
+
+The signature `hook` should be `(easy::Easy, info::Dict) -> Nothing``. 
+Mulitple hooks can be added with repeated calls to `pushhook!`.  Hooks are 
+applied in the order they were added. 
+
+The returned `key` maybe used to remove a previously added `hook` cf. [deletehook!](@ref)
+
+Examples:
+```jl
+# define hook
+hook = (easy, info) -> begin
+    # allow for long pauses during downloads (perhaps for malware scanning)
+    setopt(easy, Downloads.Curl.CURLOPT_LOW_SPEED_LIMIT, 1   #= bytes   =#)
+    setopt(easy, Downloads.Curl.CURLOPT_LOW_SPEED_TIME , 200 #= seconds =#)
+
+    # other possibilities
+      # set ca_roots
+      # disable certificate verification
+      # block or rewrite URLs
+
+end
+
+# add hook
+key = pushhook!(hook)
+
+# would fail with default download parameters...
+download("https://httpbingo.julialang.org/delay/40", "test.txt")
+
+# cleanup
+deletehook!(key)
+```
+"""
 function pushhook!(hook::Function) :: HookKey
-    global current_key
+    global CURRENT_KEY
     key = -1
     lock(GLOBAL_HOOK_LOCK) do
-        key = current_key
+        key = CURRENT_KEY
         push!(GLOBAL_HOOKS, (key, hook))
-        current_key += 1
+        CURRENT_KEY += 1
     end
-    return key
+    key
 end
 
+"""
+    deletehook!(key)
+    key        :: HookKey
+
+Remove a hook previously added with [`pushhook!`](@ref).  
+"""
 function deletehook!(key::HookKey)
     keep = x -> x[1] != key
     lock(GLOBAL_HOOK_LOCK) do
         count(keep, GLOBAL_HOOKS) < length(GLOBAL_HOOKS) || 
           warn("Downloads.jl: Hook key $(key) not found in global hooks")
         filter!(keep, GLOBAL_HOOKS)
     end
+    nothing
 end
 
 function apply_global_hooks(easy::Easy, info::NamedTuple) 
@@ -109,6 +156,7 @@ function apply_global_hooks(easy::Easy, info::NamedTuple)
             h(easy, info)
         end
     end
+    nothing
 end
 
 

diff --git a/test/runtests.jl b/test/runtests.jl
@@ -1,27 +1,6 @@
 include("setup.jl")
 
 @testset "Downloads.jl" begin
-    @testset "Global easy hooks" begin
-        trip_wire = 0
-        original_hook_count = length(Downloads.GLOBAL_HOOKS)
-        url = "$server/get"
-        hook = (easy, info) -> trip_wire += 1
-        key1 = pushhook!(hook)
-        _ = download_body(url)
-        @test trip_wire == 1
-        key2 = pushhook!(hook)
-        _ = download_body(url)
-        @test trip_wire == 3
-        deletehook!(key1)
-        _ = download_body(url)
-        @test trip_wire == 4
-        deletehook!(key2)
-        _ = download_body(url)
-        @test trip_wire == 4
-
-        @test length(Downloads.GLOBAL_HOOKS) == original_hook_count
-    end
-    #=
     @testset "libcurl configuration" begin
         julia = "$(VERSION.major).$(VERSION.minor)"
         @test Curl.USER_AGENT == "curl/$(Curl.CURL_VERSION) julia/$julia"
@@ -607,7 +586,27 @@ include("setup.jl")
         @test Downloads.content_length(["Accept"=>"*/*",]) === nothing
         @test Downloads.content_length(["Accept"=>"*/*", "Content-Length"=>"100"]) == 100
     end
-    =#
+
+    @testset "Global easy hooks" begin
+        trip_wire = 0
+        original_hook_count = length(Downloads.GLOBAL_HOOKS)
+        url = "$server/get"
+        hook = (easy, info) -> trip_wire += 1
+        key1 = pushhook!(hook)
+        _ = download_body(url)
+        @test trip_wire == 1
+        key2 = pushhook!(hook)
+        _ = download_body(url)
+        @test trip_wire == 3
+        deletehook!(key1)
+        _ = download_body(url)
+        @test trip_wire == 4
+        deletehook!(key2)
+        _ = download_body(url)
+        @test trip_wire == 4
+
+        @test length(Downloads.GLOBAL_HOOKS) == original_hook_count
+    end
 end
 
 Downloads.DOWNLOADER[] = nothing