Changes for page Multipart form-data

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27	27	* Defining the content types of each part of the message
28	28	* Construction of the complete message according to the specification
29	29
30		-To actually construct the message there a several steps needed to make it work. Luckily, most of the steps needed have to do with concepts we have already discussed in previous microlearnings. As you can imagine based on what mulipart/form-data entails we need a way to both store the meta information and the file(s) we want to send to the external party. To do so it is advisable to put the metadata in one (or multiple) header(s) and use the file content as payload. This you can achieve with a header enricher and standard transformer.
	30	+{{info}}
	31	+The following criteria apply when utilizing the boundary functionality within the multipart/form-data construction:
	32	+* The value of the Boundary must begin with a double horizontal bar –, this is called a leading hyphen
	33	+* The value of the Boundary must not contain more than 70 characters in addition to the leading hyphen.
	34	+* The value of the Boundary must not contain characters that are disabled by the HTTP protocol or the URL, such as the colon: etc.
	35	+* A boundary within the request body must always be preceeded by a CRLF line. This means that when the request body **ends** with a CRLF line an **additional** CRLF line is needed **before** the boundary doubling the CRLF lines in that part of the request body.{{/info}}
31	31
32		-Once the file content is your payload you need to make sure that the data is "raw" in nature. So when you have a base64 encoded string you should decode the string before sending it to the endpoint.
	37	+=== 3.1 Prepare the message ===
33	33
34		-On top of that we need to define the contentType header as follows.
	39	+To construct the message, several steps are needed to make it work. Luckily, most of the steps necessary have to do with concepts we have already discussed in previous microlearnings. As you can imagine, based on what multipart/form-data entails, we need a way to both store the meta information and the file(s) we want to send to the external party. For example, put the metadata in one (or multiple) header(s) and use the file content as a payload. This you can achieve with a header enricher and standard transformer.
35	35
36		-Most users would think that communication via queues to connect two separate eMagiz models is a bright idea. However, this is something that we do not encourage. We discourage this for several practical and technical reasons alike.
	41	+Once the file content is your payload, you must ensure that the data is "raw." So when you have a base64 encoded string, you should decode it before sending it to the endpoint.
37	37
38		-When looking at the practical side of things getting it configured correctly is time-consuming and an error-prone action (as is evident by the question). Furthermore, it can lead to unexpected situations where you make a typo to listen to a queue on which no messages are provided. This queue will, however, be registered on the JMS level (when you activate the flow in question with the custom configuration), which can lead to confusing queue statistics and even more troublesome false-positive alerting based on missing queue metrics or missing consumers.
	43	+On top of that, we need to define the contentType header.
39	39
40		-On top of that, when you allow one model to write and read from queues registered in another model, maintaining both models will become very complex. This holds for the ones working on the project at the moment but also for those working on it at a later stage and does that need to provide (incidental) support on the environments.
	45	+[[image:Main.Images.Microlearning.WebHome@expert-data-handling-multipart-form-data--content-type-header-config.png]]
41	41
42		-Another practical reason for not wanting this is that we do not actively support this use case from eMagiz. This means that when we update our technical infrastructure, we will not consider this scenario. This could lead to additional work in the future and reduced stability of your solution.
	47	+=== 3.2 Construct the message ===
43	43
44		-From the technical point of view, the consequence of this construction is that both models need to know each other certificates and credentials, which are not considered secure. On top of that, because you, theoretically, can exchange data from any queue to any queue, you could create a situation in which updates in one model trigger changes in the other model (i.e., when using the same data model) that are unexpected (and frankly unwanted).
	49	+After you have set the stage, you can use a standard transformer component to build your message correctly. To create it correctly, you need to take the following into account:
45	45
46		-We advise using functionality that makes it explicit that both models function independently of each other. From eMagiz, we consider two valid alternatives for this:
47		-- Using a web service as a communication layer between the two models. This web service can be REST or SOAP and has been implemented before
48		-- Using the Event Streaming functionality of eMagiz to write and read from topics.
	51	+* Each part of the message needs to be separated by a boundary
	52	+* The message needs to start with a boundary and finish with a boundary
	53	+* Line breaks are needed to differentiate between the boundary and the text content
	54	+* No line break is needed when the content is not text-based
49	49
50		-Both alternatives have the benefit that the security can be tight and explicit (i.e., only model A can write/post data to model B). Furthermore, managing the solution becomes much easier as it uses the standard functionality within the platform. Therefore, we have no plans to support this approach in the product.
	56	+Given all this, you can write the following SpEL expression that will yield a desirable output:
51	51
52		-== 4. Assignment ==
	58	+{{code}}'${multi-part-form-data.data-handling.boundary}' + headers.metaInfo + T(com.emagiz.util.Newline).CRLF.characters + '${multi-part-form-data.data-handling.boundary}' + T(com.emagiz.util.Newline).CRLF.characters + 'Content-Disposition: form-data; name="file"; filename="' + headers.filename + '"' + T(com.emagiz.util.Newline).CRLF.characters + 'Content-Type: application/pdf' + T(com.emagiz.util.Newline).CRLF.characters + T(com.emagiz.util.Newline).CRLF.characters + payload + '${multi-part-form-data.data-handling.boundary}'{{/code}}
53	53
54		-Consider what your criteria are when communicating between models and compare them to our criteria.
55		-This assignment can be completed with the help of the (Academy) project you created/used in the previous assignment.
	60	+Putting this in a standard transformation gives you the following solution in the flow.
56	56
57		-== 5. Key takeaways ==
	62	+[[image:Main.Images.Microlearning.WebHome@expert-data-handling-multipart-form-data--standard-transformer-config.png]]
58	58
59		-* Consider the following when communication between two models
60		-** Security
61		-** Loose coupling
62		-** Maintainability
63		-** Clarity
	64	+=== 3.3 Calling the endpoint ===
64	64
65		-== 6. Suggested Additional Readings ==
	66	+Now that we have constructed our message correctly, the last thing to do is call the endpoint in question. Since we have prepared our message and accurately defined our contentType calling the endpoint does not require any additional configurations compared to what you are already used to when dealing with REST endpoints.
66	66
67		-If you are interested in this topic please read the helptexts in the platform and read the following link:
	68	+== 4. Key takeaways ==
68	68
69		-* https://www.sobyte.net/post/2021-12/learn-about-http-multipart-form-data/
	70	+* Make sure to define the boundary that separates the parts of the message
	71	+* Make sure to define the content types of each part of the message
	72	+* Make sure to define the content type that matches the specification for multipart/form-data
	73	+* Construct the complete message according to the specification
70	70
71		-== 7. Silent demonstration video ==
	75	+== 5. Suggested Additional Readings ==
72	72
73		-As this is more of theoretical microlearning, there is no video accompanying the microlearning.)))((({{toc/}}))){{/container}}{{/container}}
	77	+If you are interested in this topic, please read the help texts on the platform and read the following link:
	78	+
	79	+* [[Multipart form-data explained>>https://www.sobyte.net/post/2021-12/learn-about-http-multipart-form-data/||target="blank"]]
	80	+
	81	+)))((({{toc/}}))){{/container}}{{/container}}