(SQL Server) curl with Variable Substitution in a JSON Request Body

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This example shows how to use variables inside a JSON request body using the {{variable_name}} syntax. When the HTTP request’s Content-Type indicates JSON, Chilkat automatically applies proper JSON escaping to each substituted value, ensuring the resulting JSON remains valid.

Note: This example requires Chilkat v11.5.0 or greater.

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-- Important: See this note about string length limitations for strings returned by sp_OAMethod calls.
--
CREATE PROCEDURE ChilkatSample
AS
BEGIN
    DECLARE @hr int
    -- Important: Do not use nvarchar(max).  See the warning about using nvarchar(max).
    DECLARE @sTmp0 nvarchar(4000)
    DECLARE @success int
    SELECT @success = 0

    -- Variable names are enclosed between {{ and }}
    -- Important: The variable {{var_name}} should be placed inside the quotes.

    -- This is correct:
    -- curl -X POST https://api.example.com/messages \
    --   -H "Content-Type: application/json" \
    --   -d '{"text":"{{message}}"}'

    -- This is incorrect:
    --   -d '{"text":{{message}}}'

    DECLARE @sbCurl int
    EXEC @hr = sp_OACreate 'Chilkat.StringBuilder', @sbCurl OUT
    IF @hr <> 0
    BEGIN
        PRINT 'Failed to create ActiveX component'
        RETURN
    END

    EXEC sp_OAMethod @sbCurl, 'AppendLn', @success OUT, 'curl -X POST https://api.example.com/messages \'
    EXEC sp_OAMethod @sbCurl, 'AppendLn', @success OUT, '  -H "Content-Type: application/json" \'
    EXEC sp_OAMethod @sbCurl, 'AppendLn', @success OUT, '  -d ''{"text":"{{message}}"}'''

    DECLARE @curl int
    EXEC @hr = sp_OACreate 'Chilkat.HttpCurl', @curl OUT

    -- In this example, the value we'll provide for the "message" variable
    -- will contain chars that require JSON escaping.
    EXEC sp_OAMethod @curl, 'SetVar', NULL, 'message', 'He said "Hello, world!"'

    -- To demonstrate how the variables are replaced, this example does not execute the curl command. 
    -- Instead, it generates the raw HTTP request that would be sent if the curl command were run.
    DECLARE @sbRawRequest int
    EXEC @hr = sp_OACreate 'Chilkat.StringBuilder', @sbRawRequest OUT

    EXEC sp_OAMethod @sbCurl, 'GetAsString', @sTmp0 OUT
    EXEC sp_OAMethod @curl, 'ToRawRequest', @success OUT, @sTmp0, @sbRawRequest
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @curl, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @sbCurl
        EXEC @hr = sp_OADestroy @curl
        EXEC @hr = sp_OADestroy @sbRawRequest
        RETURN
      END

    EXEC sp_OAMethod @sbRawRequest, 'GetAsString', @sTmp0 OUT
    PRINT @sTmp0

    -- The output is shown below.
    -- Notice that the quote chars around "Hello World!" are properly JSON escaped.

    -- POST /messages HTTP/1.1
    -- Host: api.example.com
    -- Content-Type: application/json
    -- Content-Length: 36
    -- 
    -- {"text":"He said \"Hello, world!\""}

    EXEC @hr = sp_OADestroy @sbCurl
    EXEC @hr = sp_OADestroy @curl
    EXEC @hr = sp_OADestroy @sbRawRequest


END
GO