Downloader: new module to HTTP fetch data

Author: benoit-pierre

ffi/downloader.lua

@@ -0,0 +1,91 @@
+local http = require("socket.http")
+local ffi = require("ffi")
+
+local Downloader = {}
+
+function Downloader:new()
+    local o = {}
+    setmetatable(o, self)
+    self.__index = self
+    return o
+end
+
+function Downloader:free()
+    self.ce:free()
+    self.ce = nil
+end
+
+local function merge_ranges(ranges)
+    local new_ranges = {}
+    for i, r in ipairs(ranges) do
+        if #new_ranges > 0 and new_ranges[#new_ranges][2] == r[1] - 1 then
+            new_ranges[#new_ranges][2] = r[2]
+        else
+            table.insert(new_ranges, r)
+        end
+    end
+    return new_ranges
+end
+
+function Downloader:fetch(url, callback, ranges, etag, stats)
+    assert(not (ranges and etag))
+    self.status_code = nil
+    self.etag = nil
+    local ok
+    local sink = function(s)
+        return s and callback(ffi.cast("uint8_t *", s), #s)
+    end
+    local body, status_code, resp_headers, status_line
+    if ranges then
+        body, status_code, resp_headers, status_line = http.request{
+            url = url,
+            method = 'HEAD',
+        }
+        if not body or status_code ~= 200 then
+            self.err = status_line
+            return false
+        end
+        if resp_headers["accept-ranges"] ~= "bytes" then
+            self.err = "server does not support range requests!"
+            return false
+        end
+        ranges = merge_ranges(ranges)
+        local ranges_index = 1
+        repeat
+            body, status_code, resp_headers, status_line = http.request{
+                url = url,
+                headers = { ["Range"] = string.format("bytes=%u-%u", ranges[ranges_index][1], ranges[ranges_index][2]) },
+                sink = sink,
+            }
+            if not body then
+                self.err = status_code
+                return false
+            end
+            ok = status_code == 206
+            if not ok then
+                self.err = status_line
+                return false
+            end
+            ranges_index = ranges_index + 1
+        until ranges_index > #ranges
+    else
+        body, status_code, resp_headers, status_line = http.request{
+            url = url,
+            headers = etag and { ["If-None-Match"] = etag },
+            sink = sink,
+        }
+        if not body then
+            self.err = status_code
+            return false
+        end
+        self.etag = resp_headers['etag']
+        ok = status_code == 200 or status_code == 304
+        if not ok then
+            self.err = status_line
+        end
+    end
+    self.status_code = status_code
+    return ok
+end
+
+return Downloader