Multiple headers only take the last one

[RinkAttendant6]

Bug Report

Prerequisites

• Can you reproduce the problem?
• Are you running the latest version?
• Are you reporting to the correct repository?
• Did you perform a cursory search?

For more information, see the CONTRIBUTING guide.

Description

Using the client's .header() method multiple times will only send the last header if several of them with the same name.

Console Errors:

No

Screenshots: [If applicable, add screenshots to help explain your problem]

Steps to Reproduce

const client = Client.init({...});

const response = await client
    .api(`/users/${upn}/mailFolders/Inbox/messages`)
    .header('Prefer', 'outlook.body-content-type="html"')
    .header('Prefer', 'IdType="ImmutableId"')
    .get();

console.log(response);

Expected behavior:

• Message body in HTML format
• Immutable IDs

Actual behavior:

• Message body in text format (default if unspecified)
• Immutable IDs

Flipping the order of the method calls will return messages in HTML format but not with immutable IDs.

Additional Context

The method only takes a string so two values cannot be passed. For example this is not permitted:

    .header('Prefer', ['outlook.body-content-type="html"', 'IdType="ImmutableId"'])

Usage Information

Request ID - Value of the requestId field if you are receiving a Graph API error response

SDK Version - 3.0.4

• Node (Check, if using Node version of SDK)

Node Version - v18.12

• Browser (Check, if using Browser version of SDK)

Browser Name - [The name of Browser that you are using for SDK]

Version - [The version of the browser you are using]

[RinkAttendant6]

This behaviour is also apparently with the Graph Explorer.

Is it possible to have multiple Prefer headers in general? If so, what is the proper way to do this?

[nikithauc]

@RinkAttendant6

Can you try the following and let me know if that works?

The values need to be comma-separated.

@peombwa Thank you for your help with this!

[RinkAttendant6]

Yes this seems to work! I suppose it would be beneficial to have it documented somewhere

[sebastienlevert]

@RinkAttendant6, I think your point is valid, though. @nikithauc what would be the impact to support a string array and a simple string as parameters and us do the work to separate them with commas? I feel this should be the SDK role to help devs and not the devs to understand the intricacies of Graph and headers...

So basically have this

interface KeyValuePairObjectStringNumber {
	[key: string]: string | number | string[];
}

versus

interface KeyValuePairObjectStringNumber {
	[key: string]: string | number;
}

Thoughts?

[nikithauc]

@RinkAttendant6 Thank you for responding!

@sebastienlevert I think this should be documented in the Graph docs as this information is relevant to any Graph API user.

Headers in most JS/TS libraries are Record<string,string>. If passing an array of strings in a popular use case in the Graph, then we should support that.

[nikithauc]

@jasonjoh Can you please guide on how to document passing of multiple values for a specific header key in Graph?